old wooden boat

[alanblue]

I have an old ply hull wooden boat, and need some advice re replacing some of the rotted internal timber framing. What timber should I use, and would any waterproof adhesive do the job?

[longliner45]

out of curiosity;how old is the boat?and what shape is the plywood in?

[alanblue]

Not sure how old the vessel is. Possibly 30 - 40 yrs ??
Hull ply is quite sound.

[CapKos]

Hi,
Use spruce or fir with the same scantling. Cut all the rot and even more. Check the old fastening. Epoxy will do the job very well. However don’t coat with epoxy the entire hull. This will not help old ply boats, just in contrary.

Good luck,
CapKos

[PAR]

Alan, Contrary to what has been mentioned, epoxy is the best thing you can do for your plywood, but is a serious commitment when the decision to use epoxy is made. The goo factor, the cost, learning curve in application, total encapsulation, etc. all should be considered.

Also contrary to what has been said, scantlings suggested on the little information you've provided is irresponsible. In short, we need more information about your boat. Frame construction, spacing, general dimensions, planking thickness, boat length, beam, draft, hull configuration, etc. to make a reasonable idea of what you have. Pictures are good. It's likely someone will recognize the boat and provide you some history about the type.

Most times an experienced wood worker will recognize the wood species and this makes things easier. Spruce is not a commonly used framing material, though some fur's are quite common like Douglas fur for example. Changing the species can be a difficult issue. The upgraded species must be of similar properties to the former or the sided and molded dimensions of the piece(s) will need to change to keep the same strength requirements.

Hi John, I got your note but lost your phone number, can you email me another?

[alanblue]

Thanks guys, your comments and time are greatly appreciated.
Will try and organise a picture, The boat is 16ft or just over 5 metres.
The framing inside ...probably ones running lengthwise are approx. 1ft 300mm apart, made from a softwood, I would figure ... most are just soft and crumbling. All the faming is about 2 by 1 inch, or 25mm by 50mm.
Someone has indicated that bending would be a probem ...I'm wondering if I could laminate sections of plywood to build up the size with polyurethane adhesive or marine waterproof adhesive.
Do so appreciate your assistance.
Alan

[PAR]

Alanblue, the members that run fore and aft are likely stringers or furniture cleats. The frames are transverse members (athwartship) and on most plywood boats, are sawn to shape, not bent. Laminating plywood for frames or stringers isn't a good idea, for several reasons. Again without knowing what you have it's difficult to prescribe a cure.

[CapKos]

With all respect to you Par, such ply boats are not constructed with epoxy-fiberglass technology in mind. Coating the entire hull with epoxy by both surfaces on such boat is impossible, and even done the humidity will continue to penetrate from the fastening. In classical hull, (without epoxy) this is no so bad since the evaporation will equilibrate the process. However if the pores of the wood are partially closed by epoxy this will be not possible and the wood will rot very rapidly. Nevertheless epoxy could be used locally for example for replacing the framing. I will not suggest using polyurethane or other type of adhesive.

So Par what kind of material and scantling you will suggest for 16 ft plywood boat ?
All the best,
CapKos

[PAR]

Epoxy has been around since the 40's and widely used since the 60's. The Goureon Brothers book on boat construction was written in the 70's and is considered by many a reference volume. This boat falls into the time frame that may incorporate these techniques. It also may not.

As for the other questions, I don't know enough about the design. Is it a powerboat or sail, displacement, semi displacement or planning, expected speed length ratio (I increase scantlings over specific speeds), etc. etc, etc.

I have several 15' designs, an outboard skiff limited to 25 knots would carry a 3/8" bottom (1/2" on a heavy duty version or if speeds increased over 25 knots) and 1/4" topsides. On the other hand I have a light weight planning sailboat that has 1/4" bottom and topside panels. Both are tape and seam constructions. A traditional plywood over frames craft may have heavier planking, and/or more closely spaced framing. All depends on the intent of the design, which in this case I know little more then it's approximate age and length.

PU adhesives have received much success, but I personally don't like them much and they are more costly then epoxy. There are also a few other adhesives that work very well in the marine environment.

[Sander Rave]

Hi Alan, it sounds like you are in the same kind of project I'm in.
Could you mail me some pics of your boat? Maybe I can be of some help but I need some details first. I can send you some if you like.
Regards,

[VKRUE]

Originally Posted by CapKos

Hi,
Use spruce or fir with the same scantling. Cut all the rot and even more. Check the old fastening. Epoxy will do the job very well. However don’t coat with epoxy the entire hull. This will not help old ply boats, just in contrary.

Good luck,
CapKos

Hello CapKos,
Why not coat hull with epoxy
I was planning to do just that.......... using CPES. Am I missunderstanding something ?
VKRUE

[Sander Rave]

It's almost impossible to make an old boat dry. When you apply the epoxy it's almost impossible to check for cracks that let water between original wooden hull and epoxy. The result is delamination in the best case. In a worse one you find out the wood is rotten all the way though before you find out.

We were lucky this winter with a B2 training sloop only to repair 1,5m of epoxy along the keel.
The bad part was next: Where did the water come from and what to do from preventing it happens again? We're not done yet... ordered a box of sicaflex and primer, but have to find a way to make a "bridge" between hull and keel on the inside of the hull. We are thinking of encapsuling foam to overcome flexing.

Just to illustrate the bother... There is a more theoretical story to back up this one, but I have to get working again.

[VKRUE]

Thank you Sander Rave.
I think that I have miss-understanding. My boat looked much like yours but probably worse. The Plywood was completely rotten and after exposing the keel found it was rotted also. Good thing that damage was limited to a section of approx. 15" - 20" or so. Removed 40" section of hull on each side of keel, removed / replaced 26" or so of keel, constructed gussets on both sides inside hull and replaced hull sections. Used white oak for keel, okume (7ply) for hull & gussets. Sealed all with CPES penetrating epoxy. This is where I think I have misunderstanding. I have completely stripped all paint from hull for repainting. I am planning to coat entire hull with CPES before painting. Boat is 46 years old, plywood, 17', 115 hp outboard. Other than damaged hull & keel (I assume is due to neglect and poor repairs by some previous owner) rest of boat is sound / great shape Pics included.
I appreciate any and all advice from everyone.
Dad taught me to listen to everybody & everything then sort out the good from the bad.

[VKRUE]

More pic's if anyone wishes to comment / question my work. All comments welcome

[Sander Rave]

Nice work! I guess that would be a step further than I would like to start from. Don't get me wrong, the picture I posted was not a plywood one, that's an other project I'm working on. I try to post those later. Keep up the good work!