Fleet a Planing Hull Version of Flint

Back in about 2003 I was asked to design a rowing/small outboard boat for operations in a short, steep chop, with the emphasis on lack of pounding. The resulting boat, named Flint, has been very successful and popular. She is very easy to build - if you follow the assembly sequence - and a distictive feature of her hull is the fine, hollow sections in the forward part of the boat. What is amazing is that this shape can be produced from a single developed plywood panel. I have tried to achieve this sort of shape in the past using conventional projection of developable panels, but the geometry required to produce a hollow shape has always defeated me. The arrival of computer programs which have the ability to do the mathematics saved me from myself!

Proof that the hollow sections come from a single panel of plywood

The very first Flint, built by Eddie Guy

In recent times I have been approached by a number of people who have wanted to build a planing version of Flint. The hull of the original rowing/sailing/small outboard version is of the displacement type, although her fine sections and high length-to-breadth ratio mean that she can be pushed faster than her theoetical displacement speed which is 5 knots. On launching day we got her to 6.1 knots with two adults and two teenagers onboard, using a 2hp Yamaha at part throttle. Steve Dorrington got his to a speed of 6.2 knots under the urge of British Seagull 40-plus - certainly an achievement!

Steve Dorrington measuring his 6.2 Seagull-knots using a GPS. Note how Steve has to sit on the midships thwart in order to retain proper trim. In the case of the planing version, a helms-person should be able to sit aft and operate the outboard without a tiller extension.

Bruce Erney, on the east coast of the USA modified his Flint to take a 6hp motor and got her up to 17 knots, I think, but he needed to put trim tabs on to overcome the tendency of the displacement hull to point her bow at the sky. I was concerned about the exercise, but Bruce had many successful trips while fishing in the big waters.

Bruce Erneys trim-tabs

One of Bruces many fishing trips in his modified Flint

Ive made a number of attempts at drawing a planing version of Flint and things were brought to a head this week when a friend/customer for whom I have great respect, asked me for a semi-disposable planing power boat which he and a friend could build over a weekend or two, to be powered by a 5hp outboard. He looked at few drawings I had on hand, and chose a preliminary sketch of a planing version of Flint, which I drew as a discussion piece for Rick Hayhoe a number of months ago.

Lines Drawing of the original Flint

Lines drawing of the planing version, now called Fleet

In the above drawings you can see the substantial changes made to the shape of the hull aft of the midsection. I have retained the fine, hollow forward sections, although Ive increased the rake of the stem very slightly in order to reduce the severity of the bending and twisting of the plywood panels. With good-quality ply the hull is easy to assemble, but some people still insist on using poor-quality sheets in order to save a dollar, and end up encountering problems - hence the alteration.

My aim with this design is to retain the extemely light and simple style of hull as seen with the original Flint, and to have her run efficiently with nothing larger than a 4hp motor. This is important in my part of the world because we can operate with up to, and including, 4hp without needing to register the boat. The customer wants to use a 5hp, and specifically asked for a water-shedding foredeck and side decks under which he can store fishing gear. He intends taking her into the open Pacific off the Queensland coast here in Australia, and so adequate emergency floatation is essential. His boat will have built-in buoyancy under the sternsheets (aft seating which extends aft in a horseshoe arrangement),  under the midships thwart, and under the large foredeck. We have not finalised details of the arrangement, but here is a very preliminary sketch with the decks and seating shown in blue.

Here is a very sketchy drawing showing one idea of an internal layout. The final version is a fair way off yet, I think. The decks have very pronounced camber to aid in water shedding (those odd looking bits at the bottom are just working drawings to establish the height of the inner edges of the side decks at each station). Note how the cambered foredeck makes the sheer look much flatter than in the undecked original - this is an optical illusion. 

This little article should give some indication of just how much the character of a boat must be changed when the mode of operation is altered. However, a completely open version with a very small motor may retain the spartan feel of the original, while still performing in the semi-planing and planing modes. When the plans are complete and the boat tested, Ill post more details. For those who want to read more about the original Flint follow this link and this link.

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Discussion about Flat Bottomed Hulls

As I expected, publication of an opinion on the subject of flat bottomed boats has resulted in some discussion. Graham brought up the matter of adequate rocker and running the forefoot above the waterline (see my previous post), and he used Phil Bolgers Black Skimmer as an example. Black Skimmer is one of my all-time favourite designs, by the way - I think she is a superb example of sophisticated simplicity, and even after thirty-one years of studying her shape and construction, I still find her to be awe-inspiring.

Here is a photo of Black Skimmer, copied from Woodenboat Magazine - I hope I havent infringed any copyright. She is close to being my absolute favourite design.

Dennis has written in with the following: -

Ross, I love it that you are discussing flat bottomed skiffs. I love em. My first sailboat was a Bolger Featherwind which exhibited the design principles you mention in your post. I am not so sure I agree about the curvature in bottom and sides. W/L length gets shortened, more of the bottom is exposed to waves and the pounding is obnoxious (this is not to say that the boat was not a blast to sail). How would John Atkins Lark (143" sailing skiff) stack up to your discussion? It has a fine entry, but the stem is immersed. It has good flare and I would bet that it does not pound the fillings out of your teeth while sailing in a chop. While I have not built and sailed another flat bottomed skiff since owning the Featherwind, I will probably do so one day because the nostalgia of that first boat has a powerful draw. Best, Dennis

I know what Dennis is talking about, and it is a good demonstration of how everything in boat design requires compromise. The shape which provides the excellent sailing behaviour (adequate rocker, matched curvature of the topsides and the bottom panel, forefoot run above the waterline) is very likely to pound badly when floating level.


There are plenty of flat-bottomed skiff designs around which have the forefoot immersed, and scores of William and John Atkin boats provide excellent examples to study. One of my favourite Atkin designs is Ration and she shows exactly what we are talking about.

Lines of Ration - courtesy of Motor Boatings Ideal Series - Chapman and Horenburger

Ration shows a rowboat which is less likely to pound in a small chop - immersed forefoot and very fine entry at the waterline and bottom - but she will still pound as soon as the waves get large enough to make the forefoot clear the water. The main problem is that the shape of the chine-line is such that there will be turbulence formed as the water running around the sides at the bow inevitably runs down and across the chine, and subsequently runs back across the chine in the aft sections (although this will be less of a problem than at the bow). A mitigating factor in this design is that the boat is relatively slim. It is in wide, flat boats that the problem is at its worst, causing excess drag and wild, unpredictable steering - particularly downwind.


To get an appreciation of what Im trying to describe, compare the shapes I show below: -

A typical flat-bottomed skiff with the heel of the stem immersed, and the bottom of the transom coming to above the waterline. Im only showing the body plan here, but the boat Ive drawn as the example is fairly long and slim.

The same boat heeled 25 degrees. In reality, the stern would probably be forced a bit higher and the bow lower than Ive shown here, which would make matters even worse.

A clearer view of the same boat. See how the chine line will generate turbulence and drag, and will tend to force the boat to round up.

For comparision, here is the underwater shape of the example I drew for the previous posting. While this is not a perfect shape by any means, it is vastly superior to the example shown above - but it will pound more when flat in a ripple.

It is all a matter of degree - the Featherwind mentioned by Dennis shows close to the ultimate in matching the curve of the topsides and the bottom - at least for a sharp-bowed boat - but she is best used as a sailing boat, or a rowing boat on flat water.

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What is a hull and construction categories

Dave Mainwarings definitions

HULL defintion of:
The outer shell, including frames, ribs, interior bulkheads, exclusive of masts, rigging, deck and equipment.



"bare hull" defintion of:
A model boats outer shell, EXCLUDING, ribs, interior bulkheads, exclusive of masts, rigging, deck and equipment. Example. A fiberglass hull as pulled from a mold.

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A wooden hull:
one constructed of wood (including plywood).

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A glass hull:
one constructed of reinforced plastic (cloth impregnated with resin). Nominally referred to as a fiberglass hull.

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A composite hull:
a hull constructed of wood and covered with reinforced plastic (cloth impregnated with resin).
OR:
a hull constructed using a laminate (sandwich) consisting of reinforced plastic (cloth impregnated with resin) on two sides of a core . Core materials may be foam or wood.

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Fitting Different Rigs to an Existing Boat

One of the great joys of owning and/or building a small wooden sailing boat is that there is plenty of opportunity for experimentation. For some reason it doesnt seem right to go shifting things around on a glass production hull, but wooden boats lend themselves to modification. With high-quality epoxy and fastenings, the end result should be as good, or better, than the original work.

Ive mentioned previously that rig modification was something which interested me from before I left school. I had been brought up sailing racing boats at the local club, all of which had modern, deck-stepped rigs with lots of stainless-steel fittings and sails full of batten pockets. Although I loved the sailing, I felt the urge to cruise alone in a boat fitted with a more simple, traditional rig such as a standing lugsail.

Phoenix at about age 20 with her original rig

For me, the first real experiment came when I converted the cruising dinghy my Dad had designed and built. She had been constructed with a deck-stepped Bermudan rig just like all of the racing boats Id sailed. She was (and still is) a fine boat, but I got it into my head that Id re-rig her with a Chinese Lugsail (a.k.a. Chinese Junk Rig). I spent a long time on the calculations - far too long, I believe - but that was because I didnt really know how accurate I had to be with all of the proportions, and I was particularly concerned about the location of the centre-of-area of the sail in relation to the centre-of-lateral resistance of the boat.

Phoenix showing how well she could get to windward with her Junk Rig. A nice day in tropical North Queensland.

Accelerating out of the tack and heading off hard on the wind. This rig was exceptionally easy to handle, reef, and furl, and has been one of my all-time favourite rigs. I will be making another one sometime...

After the Chinese Lug rig, I fitted the same hull with about four or five other sail configurations, finally settling on the Balance Lug which she currently carries.

When I designed boats such as Phoenix III, First Mate, and Periwinkle (and some others which have not yet been published), I decided from the outset that I would arrange the rig proportions so that several different rigs could be used on the same mast(s) and/or using the same mast step and partners. This results in boats which can be rigged in a number of different ways without having to make any physical alterations to the structure of the boat. I have already spoken about this a little in my post about Phoenix III and the Perfect Customer 

Here are some more photos to illustrate what I mean.

John Shrapnels Periwinkle showing her standard Cat Ketch (Periauger) rig. Crew weight is a little far aft, but she is going nicely. This boat is very fine up forard, and needs to have weight kept out of the bow when pressed.

Same boat, but with the mizzen removed and the mainmast and mainsail moved aft to another mast step and partner. The rig is still perfectly well balanced, even though the 51sq ft mizzen has been removed entirely.

Here she is with just the mainsail up, stepped in the middle location, but with a substantial reef tied in. It may look calm in the little bay, but it was blowing outside on the more open water.

When it really starts to blow, or when the crew weight is low, you can set the mizzen in the central location. Once again the hull balance is fine, but the rig has been reduced to a snug 51 sq.ft. Even so, when this picture was taken, the boat was doing 8 knots by GPS! If you needed to , even this sail can be reefed.

This shows you the rig combinations on paper. Note how well the centres-of-area cluster near the centre-of-lateral resistance of the hull in all combinations. The key to this was careful proportioning of the sails and the mast locations.

This is another rig which can be used on the boat. The little flying jib is optional, but will help her a lot and will stand ok without shrouds or backstays. The gaff-headed cat rig is set on exactly the same mainmast as in the standard rig, so there is no alteration required to any part of the boat. This print is of an early sketch and some elements are not shown.

...and her you can see Graham Faulkners Periwinkle with the Gaff-Cat rig, beachcruising on Fraser Island, Queensland, Australia (this was the second boat built, and Graham even made his own sail!)

This shows the three mast locations - the mainmast partners in the lower/left of the photo, the central position through the main thwart, and the mizzen partner through the stern sheets (aft thwart)

All of that thinking made me very tired! Actually, that is just me showing the comfortable sleeping position on either side of the centreboard case.

Build yourself a wooden boat, and then try some rig experiments - it is great fun.

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CNC Boat Kits and Prep for the Maine Boatbuilders Show

It has been very busy as evidenced by fewer postings. We have launched a new website for the CNC Boat Kit business www.CNCboatkits.com

ClintChaseBoatbuilder.com will feature the boatbuilding, mast and spars, and oars work.

One of the most important details in a good CNC kit is working out the NC scarf. Here is a CNC router cutting some test scarfs.

 

The router above is using a 1/4" bit to follow lines of code generated by computer software. The code is specific to a .dxf file for the part, in this case a scarf joint.

 

The dogbone shape you see is the key, literally, in that it locks the scarf together and aligns the entire plank. When a builder receives a kit, all the planks are precut to the precise spile and sweep of the plank but it short segments. To preserves the proper shape, this NC scarf needs to be right on the money.

 

The beauty of this scarf is that it is blind, covered up by the outside plys so that it is not seen from the outside. This would be especially important for varnished planks.

We are very busy getting ready for the 2010 Maine Boatbuilders Show in less than a week! We will be in building #2 on the left as you enter from the main entrance direction.

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S45 Class Sailboat Plans line drawings on line

Model Sailboat Plans on line

Most browsers will allow you to right click and open the jpg images. You can then save them to your machine.

This set of plans are based on drawing from John Fisher 2006. John may have new and updated drawings available. Check with http://groups.yahoo.com/search?query=star45 membership required.

I want to thank J. Herrmann, www.graphicLanguageOnline.com, for his assistance in converting pdfs to jpg drawing, adding color to the templates and adding the grid to the final images

You can print these drawing to many different sizes.They are not necessarily to scale.

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La Paz to Bahia de Concepcion

Ensenada Grande with mainland Baja in the background.

On Saturday, April 13^th we went grocery shopping at the local Mega, took a long swim in the pool and had dinner at Steinbecks. The next morning we checked out of Costa Baja and headed north to Isla Partida. In the Sea of Cortez the wind generally blows up the sea or down the sea. Today it was blowing down the sea so we motor-sailed directly into a 15 knot headwind and lumpy, choppy seas as we passed up the west side of Isla Espiritu Santo toward our destination of Ensenada Grande on the west side of Isla Partida, arriving in the late afternoon. There were a few other boats in the anchorage, but it’s a big enough bay that we were able to anchor in a fairly secluded spot close to some bluffs on the south side of the bay. The water was clear enough that I could see the anchor send up a cloud of sand as it hit the bottom 22 feet below the surface. This made the snorkeling great, and we saw lots of tropical fish and healthy looking coral. Later we took the dinghy around the southern end of the bay, past Punta Tijeretas and into the tiny cove of Las Cuevitas where there is a blue footed booby rookery. It’s not the nesting season now, but there were still a lot of boobies around. That night I set my alarm to wake up at 0200 so we could watch a total eclipse of the moon. There is something awesome about seeing a lunar eclipse from the deck of a sailboat where there is no light pollution from any nearby civilization.

Sunset is a perfect time for a paddle in Ensenada Grande.

I have no idea how these unusual rocks were formed but they are fascinating to explore.

While there, we hiked up the hills behind the bay and explored the strange rock formations that line the north side of the bay. When we got restless we sailed north again toward the fishing village of San Evaristo on the mainland of Baja.

With a nice breeze out of the southeast, we had a pleasant sail for about twenty miles then about six miles from the anchorage, the wind died and we began to motor. We had been trolling all day without a bite, but about four miles out, the reel lit up and we caught a 20 pound dorado.  This was our first fish of this kind and as soon as we got the anchor down in Evaristo I had the BBQ out and we had a fine meal of grilled dorado, wild rice and a fine bottle of pinot grigio, supplied by my friends at C1. Thanks guys!  We spent a couple of days in Evaristo then departed for Puerto Los Gatos, about thirty miles up the Baja coast.

We caught him just in time for dinner.

A dorados beautiful colors quickly fade when they die. After giving him a couple of shots of rum this fellow relaxed and died peacefully.

It was a beautiful starboard tack reach, with about 12 knots of wind out of the east under a hazy, somewhat overcast sky. I like the overcast because it provides some relief from the sun, which can be brutal here in the Sea. We approached Los Gatos from the southeast and saw a boat anchored in the far northern part of the bay, which is about half a mile wide. We anchored in the southern part of the bay, about as far from the other boat as we could get and were looking forward to a beautiful, quiet evening.  But within an hour three other boats came into the bay and anchored close enough that we could hear them talking as they enjoyed their sundowners.  A couple of them left early the next morning so we were able to explore this beautiful bay pretty much in peace and solitude. Different voyages have different flavors. The last time we were here, three years ago, we were delighted to have lots of friends from other boats around. This time, we have been inclined to seek the solitude of empty bays and quiet nights. 

Our dinghy is a speck on the beach at Los Gatos.

On Saturday, April 19^th we got the anchor up early and headed for Bahia Agua Verde, about 13 miles north. With three knots of wind out of the southeast, there was no point in trying to sail, so we fired up the diesel and a couple hours later we anchored about a hundred yards off the beach in Agua Verde. Since it was the day before Easter Sunday, the beaches in the fairly large bay were crowded with Mexican vacationers here to celebrate the holiday. The next morning we hiked into the country behind the little settlement. Aside from fishing, the locals raise goats, pigs and a few cattle. There is a school and church, along with a couple of small tiendas and a restaurant or two, so Agua Verde, though it has no cell phone or internet service is fairly cosmopolitan compared to most other places in this part of Baja California.

Later in the day we raised the anchor and continued north 22 miles to Puerto Escondido.  We arrived around 1700 and passed through the narrow channel into the lagoon that makes this place an excellent all weather port of refuge. The lagoon is over a mile long and half a mile wide and until recently had over a hundred moorings. Now there are only a few moorings left, and they don’t look well maintained. Ashore, things have declined from the last time we were here. There is still a boatyard with a Travelift and a floating dock and a few boats hauled out here, but the place is pretty desolate. The restaurant has closed down and so has the little tienda. Puerto Escondido should be a thriving community, but apparently there has been a lot of disagreement within the local business community and with the government which has had a bad effect on the village. We had hoped to stock up on fresh food and use the Internet here, but instead we spent one night in the lagoon tied to an iffy looking mooring and left the next morning for the town of Loreto, about 14 miles up the coast.

Puerto Escondido sunrise. Regardless of the business situation in the village, the scenery remains awe inspiring. 

There is a tiny harbor at Loreto but it is for the exclusive use of the local fishermen, so we anchored outside and took the dinghy into town where we had a nice meal at the Hotel La Mision, checked email and wandered around the town a bit before heading back out to the boat. While ashore we visited a unique museum of sorts, with the skeletons of whales and dolphins on display.  Back aboard Finisterra, we spent a peaceful night anchored outside the harbor, then left early the next morning for Caleta San Juanico.   

 The distance from Loreto to San Juanico is about 27 miles and with scant wind, we motorsailed the entire distance, arriving in the early afternoon. There were four or five boats anchored in the north end of the bay and a couple more at the south end, so we chose a nice spot just off the beach in the middle part of the bay, anchoring in about 15 feet of water. With a light breeze coming out of the southeast and crystal clear water, the swimming was delightful. Later we grilled the last of the dorado I caught a week ago for dinner. The next morning we were underway early for the 50 mile passage to Bahia de Concepcion.

Caleta San Juanico is dotted with rocky islets.

 The wind blew out of the northwest, exactly the direction we wanted to go, so we motored toward Punta Concepcion until we were a few miles out. Then the wind shifted to northeast and piped up to about 20 knots and we had a fast sail around the point and about six miles down the bay. Then we furled the sails and picked our way through the pass between Punta Piedrita and tiny Isla Pitihaya, toward Playa Santispac. There were several boats already at anchor there, so we bore away toward the little cove at Posada de Conception where we anchored in about 20 feet of water in the lee of some tall bluffs which offered good protection from the strong northerlies that sometimes blow down the Sea of Cortez. Finisterra was to remain at anchor here for the next nine days. 

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Banderas Bay to Mazatlan

Finisterra finally sailed from La Cruz around 0900 on Sunday, March 30th bound for Mantanchen Bay and then Mazatlan. It was a beautiful morning with a light offshore wind early and the promise of a nice beam reach to Mantanchen in the afternoon. We motored out around Punta de Mita and turned northward in almost no wind, but by noon we had enough wind to sail. We hoisted the main and set the jib and settled down on the reach to Mantanchen in about 10 knots of wind. It was looking like a beautiful day-sail all the way.

Mantanchen Bay sunset

Shortly after we got the sails set and trimmed, I heard a strange creaking noise coming from somewhere down below. This was a new noise, not the typical creaks that I was accustomed to. I searched around the boat in all the likely places that creaks might come from, but couldnt find the source of the noise until I opened the starboard lazarette hatch. When I looked down into the compartment I noticed that the bracket for the autopilot ram was moving back and forth in an unusual manner. Then I realized that the bulkhead was flexing and the joint where I assumed Beneteau had spliced or scarfed together two pieces of plywood to make the aft bulkhead was not a joint at all. It was not lapped or scarffed, or even glued together. Nope, Beneteau apparently saw fit to just butt the two pieces of plywood together without the benefit of any adhesive or mechanical fasteners. Then whoever installed the autopilot ram drilled the mounting holes less than a quarter inch of the edge of this imaginary joint. The bracket was mounted with massive 7/16" bolts and a stainless steel backing plate so it looked like a proper job, but looks can be deceiving.

By mid-afternoon we were gliding into Mantanchen Bay and got the anchor down in about eighteen feet of water three quarters of a mile from the beach, which I hoped was well beyond the range of the no-nos that live around here. Then we had a decision to make: We could go back roughly 50 miles to La Cruz or continue on to Mazatlan, another 130 miles north from here. After looking at the weather forecast we decided to press on to Mazatlan. The wind would be on the nose the entire distance but it would be light most of the way. We would be motoring into it and that would put the least stress on the wobbly bulkhead.

Mountains behind Mazatlan at dawn.

To put this little problem into perspective, we were in no danger and the worst that might have happened to us was that we might have to hand steer if the bulkhead failed completely, which was very unlikely. But it certainly annoyed me as a boatbuilder that the boat was built in this manner. And of course the problem needed to be fixed before we ran into any real weather, which is always a possibility in the Sea of Cortez.

View from the aft side of the bulkhead.  When I replaced the autopilot ram back in 2012 I assumed this joint was lapped but its not.

View from the forward side of the bulkhead.

The repair was easy enough. I went over to Marine Services Mazatlan, which is located in the shipyard next to Marina Mazatlan and had them cut out some plywood reinforcements that I bonded to both sides of the bulkhead with WEST epoxy. Once the epoxy cured it was a simple matter to reinstall the bracket and ram.

Both sides of the bulkhead were sanded and prepped.  

Plywood reinforcements bonded in place. The screws were used to clamp everything together while the epoxy cured.

Bracket and ram reinstalled and ready to go.

With the repair completed, we were able to spend some time around the pool at the marina and wander around the beautiful city of Mazatlan. In a few days well head northwest across the Sea of Cortez to La Paz.

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