Building the Hull - Đ Frank Ellinghaus -
new Nov. 2001 new Dec. 2001 last update Dec./27/2001
Building the Boats Hull
The Boat Plans
There are good reasons to rely on the
experience of proven boat builders/designers with planning your dream project.
You will avoid some of the pitfalls of poor boat design and some beginner
mistakes. When looking on the outcuts of my boats chines (and thinking could
this really fit together?) I realized that I wouldnīt had thought of this shapes
in my somewhat two dimensional way of thinking. But the boat was going to be
three-dimensional and trying to find the forms out through try and error would
have cost me a lot of unnecessary cutted wood and wasted time.
A common problem for new boat builders arises when they get the plan and realize, itīs not so simple as thought. If you
get your plan with a table of offsets and no patterns, you can expect the same
problems as the building aspirant in this
rec.boats.building thread. It would be a good precaution to look for a book which describes how to get the boatīs lines onto the plywood panels. You could ask the designer when ordering the plans how you are supposed to do that. If itīs with the help of a table of offsets you could order the book right away with the plans or get it from your library - before the plan arrives. A book which describes the lofting / laying out process, is "Small boat building" from Dave Greenwell. Looks like a fine book to me - but there are a lot of others. You can use my search-section
for a book-search.
My Boat PlanI
found my plan at bateau.com. The V12 Dinghy has a beautiful
hull, 12 ft. long and 4 ft. 6 inch wide. Just the size I could handle. Since I
wanted a bigger sail I did "design" my own sailplan and spars. It worked out
fine for me.
Free Boat Building PlansHere are some free
plans links. This is also the fastest way to get your plans, simply
download them. On the other hand - if you are the type of person who takes pride
and satisfaction in planning all on your own, youīll find free boat design
software with this free
boat design software links.
Commercial Boat Building PlansThe vast majority of plans
is provided by designers who charge about $ 20 to $ 80 a piece for small to
medium boats. You may need some more time to get it since the designer wants
your money first :-) and usually sends it out with snail mail.
vendors often provide patterns or even kits with precut bulkhead, bottom and
side hull parts. But this kits look rather expensive to me since they take a
great chunk out of your savings through self building - while saving not as much
of your time.
Most professional designer plans should be proven designs
with some boats out being built before. Some provide plan catalogues and you can
choose from a variety of designs. Since I am more in the "cheap" direction I
like to point you to other places for commercial plans like the Open
But I also like to link at this place to two (I
would say semi commercial) boat plan sites which charge very modest premiums for
Carnell with his $ 20 plan for the $ 200 sailboat a 15ī-6īī hull and his
sea skiffs from 18 to 22 foot.
Michalak with his two boat catalogues you can order for 4 $. I bought one of
his designs (yet to be built), Larsboat a kajak for two person, for 20 $ and the
plan looks very clear and simple to me.
If you are looking for a special boat or one you already know, Chuck Leinweberīs Duckworks Magazine features an comprehensive Index of Links to home buildable boat plans and projects on the WWW. For boat plans in book form, youīll find links to the Amazon. com website for online ordering.
Lofting / Laying out - or how to get the plans drawings on the plywood?
In former days the boat builders would take strategic points of
their plans lines and bring them to full size on the floor through connecting
this points with flexible battens and scribing the curves at their edges. More
points would mean exacter lines.
Lacking more sophisticated equipment a
typical garage boat builder has to rely on this very technic (bringing the lines
directly on his plywood panels) or on paper patterns the designer delivers with
How would the profies do this now? I think nowadays theyīll
start their cutting-plotter and let him cut the patterns out full size or use
their old wooden patterns, they used hundred of times before. That probably was
in the mind of my boat`s designer when he wrote that drawing the panels would
take only 1 1/2 hours. Unfortunately I was a beginner and needed a lot
of time to figure the meaning of the plan and patterns not delivered as one
piece patterns as I hoped.
Than I had to go out buying wrapping paper and
blue print paper to scribe the lines from the so called "patterns" which came in
form of several parts of pattern lines for several hull pieces on two piece of
paper. This numerated lines had to be put together correctly to draw the real
patterns used on the plywood. This took also a lot of time, to figure the
pattern-system out. Itīs like a puzzle which is fine if you are in games at this
time - in my case I was rather in boat building. I would have gladly paid some
more dollars for one part ready patterns. The money the designer saved on paper
costs with cramping this all together wasnīt worth the time I lost.
designer state that laying out from the plans given dimensions is the more exact
way to go since paper patterns could shrink or expand. But nevertheless they
provide patterns knowing they would lose business if they wouldn`t. If you want
to use patterns, ask the designer if he delivers full sized patterns drawn on a
separate piece of paper for each panel! This would be the ideal way to save you
||Here the designer "patterns" are clamped on the edge of my
plywood panel. Underneath is blueprint paper and under it wrapping paper.
I used a glass cutter to scribe the pattern lines onto the wrapping paper.
The cut outs from the wrapping paper than became the real patterns for the
bulkheads, transom, bottom parts and side parts of the hull. |
The Boat Building Materials
The hobby-boatbuilder often uses plywood and epoxy (with filler and fiberglass cloth for the seams) as his prefered boat building materials. Plywood is cheap and epoxy (which is not so cheap) is good for strong seams and sealing the wood. Polyester was used more often in former times but less nowadays, since it doesnīt seal very good and the boat would start to delaminate faster. I needed about 6 sheets of 4 x 8 ft. plywood for my 12 ft. dinghy and a lot more epoxy than thought because I sealed the boat two times.
Paint is the third biggest position in the material bill for the hull and the rest is rather minor.
Ways to bring the costs of hull building significantly down are:
1) Use of regular plywood for outsides instead of marine plywood, (I did it and so far the boat is ok, but there is no warranty for you).
2) Using epoxy for seams only and not for coating the whole hull with it or alternative at least coating only once not twice. I would seal only once if building a boat again. This does not only save money, it saves you also from epoxy noses running down your hull after sealing the second time. With the first seal the wood sucks the epoxy in, so the danger of running noses is not so big.
3) Painting the hull with acrylic house paint for outsides and not with expensive marine paints. (This is what I would try for myself the next time). new Take a look on Dave Carnell`s article about using acrylic house paint.
To get some insight about the contrary opinions on using acrylic house paint (or latex paint) take a look into this newsgroup thread.
At Dave Carnellīs site you find also his Epoxy Knowhow" were he writes about using pulverized limestone from fertilizer for a nickel a pound as a filler for joints. This would even save some more bucks on your hulls costs when using it instead of the micro fillers from epoxy merchants.
Exterior grade Plywood is sold in 4 ft. x 8 ft. panels at Home Depot or similar. It probably has not the strength of marine plywood because of the sometimes bigger or more frequent voids in the inner layers but it is glued with the same water proofed glue as the marine wood. Donīt use plywood for insides. It would delaminate quickly.
The four plywood types in USA are moisture resistant (MR), boil-resistant (BR), weather- and boil-proof (WBP) and marine plywood (MP). Plywood labelled MP or "resin bonded" should be avoided.
So what to do if there is no label or it is not US-plywood? When doing a newsgroup search on plywood for boatbuilding you will hit on the boiling solution. Boil a peace of the plywood you want to use for your boat for some time. If it doesnīt delaminate it is more likely that it also resists delamination better when time passes. Some would and have said you donīt boil that often your boat. I wouldnīt recommend that either. But if you want to use cheap plywood boiling a peace of crap could save you from spending a lot of time on a soon rotten project.
For further information take a look on Craig OīDonnelīs Plywood for Boatbuilding FAQ.
Epoxy is cheaper as in marine stores when you buy it online. Here are some vendors from my Link-Page. One of them, Raka Inc. let us take a glimpse into itīs "Epoxy User Manual" online.
The Plywood Boat Building Method
Using plywood for hobby-boatbuilding is a time- and cost effective method to get to results. Methods like "stitch and glue" or "tape and tack" boil down to a sort of bending the longer hull parts (bottom, side parts) around and fixing them at bulkheads and stern of the boat. For stitch and glue copper wire or plastic fasteners are used to "sew" the parts together while the first fixation with tape and tack goes through tape and screws, nails or with a tacker.
If the hull is around or even longer than 8 ft. you got to have length of more than the 8 ft. which standard panels provide.
The butt joint seems to be the easiest way to get longer panels. Dave Carnell specialises on the invisible butt joint at his site, while Jim Michalak describes in his article "Joining Plywood Sheets" several ways of joining.
My V12-Dinghy is designed for the stitch and glue method. I couldnīt resist to change it a bit to stitch and glue and screw since I feel more comfortable with some screws holding the construction in the first place. But I am aware that the pure stitch and glue method getīs at least the same strength and saves some weight too. So take a look at the pure stitch and glue method at the designers website.
| hobby horse
I guess you donīt want to get a hurting back while working at the boat on the floor. I custom made this hobby horse for the V12 building process. The hullīs "V" holds the hull on the horse when upside is up. When turning the hull upside down it is possible to lift the boat at one side and roll it over alone on it not needing a second person for the turning process.
Cutting the Plywood Parts For me using patterns worked even if
I lost time. Should the boat be an inch longer than planned, what does it matter
when all parts are expanded equally? I think itīs more important to get the
halfs equally formed. For that you can cut one panel (for example left bottom
panel) first and take it as the pattern for the second panel (right bottom
panel). Than clamp both panels together and fair them to their exactly equal
||Using two hobby horses with two 8 ft. 2 x 4īs layed on it,
I could cut the plywood panel without having it bowing to much. The best
way for cutting is using a circular saw with the blades adjusted that they
are just cutting through the wood (not to long). When used this way the
circular saw is superior to a jig saw. |
The Butt Block new
| Having cut out all boat pieces from the plywood the next step is joining fore and aft halfs of bottom and side parts.|
A very strong and yet easy to accomplish joint is the "butt block". If you do it right the parts wouldnīt break in the joint but in the nearby wood when loaded. The parts are pushed together bluntly at the edges. The joints strength comes from the epoxy-filled fiberglass tape around the parts.
Placing the Butt Block Joint new
You just brush the joint edges with epoxy, put the parts together, brush fiberglass tape with epoxy, wind the wetted tape around the joint and let it dry.
Sounds easy? It is, if you do it like this:
1. Step:Mixing epoxy (resin, hardener and filler) for glueing/taping as your epoxy manufacturer recommends.
2. Step:Cutting a long fiberglass-tape that is at least 2 1/2 times as long as your seam.
3. Step:Brushing the fiberglass tape until it is completely filled and place it on a piece of polyethylene film on even ground.
4. Step:Wet the joints edges, place them onto the fiberglass tape - ends on both sides not covered.
5. Step:Wrap both ends overlapping onto the seams upper side.
6.Step:Cover this with polyethylene folie and place some weights onto it until the joint is cured.
||This photo shows the side parts, butt block already cured with some ledges glued on for bulkhead placement. Bottom parts with what I could find as weight, butt block in curing process.
The Bulkhead with Stern new
||Bulkheads and transom are the framework of this boat. They provide itīs shape since sides and bottom parts bend around their edges.
The photo shows the side parts already bent.|
On this boat the designer assigned the first bulkhead exactly at the butt-joints which gives it some extra stability.
Using the pure Stitch and Glue method you would drill holes and "stitch" them together with wire or plastic fasteners.
I used some ledges glued to the bulkheads edges and to sides and bottom parts to screw them together. Since I had no help to hold the parts when assembling I wouldnīt know how to get this done without some screws.
The Skeg/Keel new
||The boats plan asked for a skeg fixed onto the outside of the bottom part. I chosed a lengthened skeg mounted directly on transom and bulkheads. The bottom parts got a cutout for the skeg/keel and are fixed also from inside and outside of the bottom with epoxy-tape. |
Since it looks somewhat like a keel to me I call it skeg/keel. It is from solid oak and takes a lot of scratching without pain when pulling the boat out of the water.
The Stem new
Stem with tips of the side parts "sewn together" with wire. In the middle a piece of solid oak. The holes for the wire are drilled through side parts and oak piece. From inside it is later further strengthened with epoxy filled cloth.
The Raw Hull new
Isnīt it a beauty? Looks like a real boat!
At this stage I thought, most of the work was done. But I had to realize the bigger part of it had yet to come. When the parts have been assembled the seems first get covered outsides with some sort of tape for instance duct tape.
Than the boat has to be switched over and the seems can get presaturated with epoxy resin. Thereafter theyīll have a filling with epoxy putty. The last task on the inside seem is to cover the filet with wetted fiberglass tape.
When the inside seems are fully cured switch the boat again, remove the tape and cover the seems on the outside with epoxy filled fiberglass tape.
The Dagger Case new
If you want to build a rowing boat only you donīt need a dagger case. You need it only for a sailing boat. But it is not a big deal to build one and not using it in the end. The already installed dagger-case will come handy when you feel the itch to sail and I guess this moment is almost certainly to come.
It is made from two ledges and 1/4 inch plywood. You have to cut out a hole into the boats bottom, fit it in and fasten it with epoxy filled tape at bottom and bulkhead. The seat or seat plate will be mounted onto it and getīs a slit for the dagger board.
Seats and here the seatplate give the structure a lot of strength. But
my plan did not provide measurements for accessories like seats only suggestions how they could look like.
Only the structural parts of the boat hull was delivered. Chances are this could be the
same for other plans. So you are likely to be the designer of your boats
I measured the shape of the seat plate and as well for the deck with wrapping paper. You can get
large rolls of this stuff at places like Office Depot for example. Its a great
help to find out the exact shape of the deck plate. Simply lay it on the place you want to fit in the part,
if possible clamp it on and scratch it with your fingernails or a nail on the
underlying edge. Than cut this paperscratch out and use it as pattern to
draw the lines on plywood.
I didnīt build separate seats but one big seatplate. This sure
adds some weight to the boat and reduced the size of the cockpit in my case a
bit too much. I since have cut out a big chunk off the plate when taking the boat home
after the first sailing year. I wouldnīt recommend a seat plate like this for someone who builds the same boat
(the V12 sailing dinghy). Only in a bigger at least 5 and a half foot wide boat this would make sense to me now. The plate uses too much space for this little dinghy. For the V12 just stay with two separate seats aft and in the middle.
plate is made of two layers 1/4 īī plywood. The left picture shows the first
layer. The first layer is made from 4 parts since itīs almost impossible to
measure all at once. The measurements were taken with wrapping paper as for the
The layers 4 parts are glued to one piece using the butt joint
procedure. This means all pieces are put together as they are without scarfing
and connecting all parts on both sides through 2 layers (in this case) of cloth,
filled with epoxy. These cloth-epoxy-joints should be as strong as the plywood.
You find more about this method on Dave Carnells homepage , look under
"Invisible Butt Joints".
Iīve put this first-layer-plate on two ledges,
crossing both bulkheads. But this isnīt a must. It was caused through my
decision to set the seat a little higher than planned before. If you get the
dimensions right in the first place you donīt need those ledges. After placing
the layer on the ledges I glued the plate with epoxy-filled cloth to the hull
To get the measures for the second seatplate layer was simple,
since the completed first layer could be used as a pattern. Glueing this on the
first layer was no big deal. After filling the voids on the side with epoxy
there was a strong bond to the hull and the completed hull got a very stiff
The slit in the fore part of the seatplate is for the dagger
board. The two rectangular holes aft are used to insert tupper ware boxes which helps
to store some smaller things safely.
Seatplate set onto the bulkheads. The two ledges fastened at the bulkheads tips are like handles and a good help to carry the boat side by side.
The Deck new
The deck plate is made of two 1/4 inch
plywood pieces. The shape was measured with wrapping paper layed over the boats tip as used at the seatplate as well.
The first plate put on the hull edges and on inwales which have
been screwed and glued on before installing the deck. The screws are covered
with epoxy later so you can let them in their holes.
Screw (into the
inwales) and glue this plate from upside down. After that you can get a stronger
connection through laminating a tape on the plates edges and covering the
gunwales. Than the second plywood plate should be put on immediately. This will
cover the disturbing tape on the decks surface. The slant edge on the sides is
filled with epoxy putty.
Sides and Gunwales new
The upper tips of the gunwales and the boats side are covered with a small two layer plywood-plate. |
This would make a good seat to lean out, I thought when I planned to do it that way. Now I have to admit I never used this possibility since it would have to blow pretty hard and constant to avoid me capsizing against the wind with this small boat. Nevertheless it does make the sides very stiff and I would cover them again with a plate.
I do have even an idea to combine the sidewards cover plate with a swimming noodle to get a cool "capsize-avoiding-device" and rubrail. I did not build it yet since cutting the old cover plate of my V12 off to install a new one would be a mayor task. But perhaps could someone who is building the boat now use this idea? (and give me a hint how it worked out).
If the boat is going to capsize and the side is even with the water line, the swimming noodle can get fully under water without one drop of it coming inside. The cover plate holds it off.
Rick Bedard used a swimming noodle on the gunwales of an 8ft OSS Dinghy (Rick Bedardīs flotation noodle).
He writes: "My 60# kid sitting next to the side bearing down with all his weight could not put the rail under."
In his case the noodle was only fixed onto the tip of the side - not leaning out sidewards as in the drawing above. The flotation could even work better with the device sitting outside the hulls body.
boat to launch