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Bulkhead attachment, stringers, and weave fill? :)

Hello fellow Wharram fans!

I’ve been messing about with a Tiki 30 for years. Have not made much progress, just getting to installing the bow bunk in the starboard hull.

Anyway, I have a few general building questions that I would greatly appreciate any answers to. I’ve built and repaired a couple small boats and a kayak. In those I’ve always taped the seams and bulkhead joints to hulls/floors etc. I’ve been doing the deep dive on the Tiki docs, an in the “Building Instructions” Page 3 there is a materials listing for 100m of 150mm glass tape (175g/m2). But I can’t find anyplace where Wharram says to use the tape other than along the keel sides. I’m using 6oz 6inch tape on the lower hull/bulkhead joints. So is this overkill or correct?

Next is filling the weave of cloth and tape necessary. Where aesthetics and UV are not a concern, does the weave need to be filled? I normally pre-wet the plywood then apply the cloth and done.

And for the trifecta, Are stringers/stiffeners good with just the epoxy glue behind and very small fillets, just enough to ensure no gaps? Or are larger fillets good? Or is glass cloth over them needed for proper offshore use?

Hope you read this whole question, and staying warm if you in the north(0F this morning) :) I apologize if need/should separate questions.

Thank you!

OC

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"So is this overkill or correct?" - IMO it is overkill.Building instructions booklet, Making Epoxy Fillets chapter, paragraph 5, only thing required is "Coat the sanded fillet with epoxy resin to seal it". Then again, you may always build a heavier boat than what the designer intended, the only issue will be you won't be able to carry as much load.

"does the weave need to be filled?" - Building instructions booklet, Coating With Epoxy chapter, Laminating : "you need to fill the weave with the right amount of epoxy and remove all air".

"stringers/stiffeners" - I checked the Building Plan Book and the Building Instructions booklet, as well as the plans, maybe I missed it but I saw not even fillets required for stringers/stiffeners, just glue.

My choice would be to trust the designer unless somebody informed of a concrete and definite failure in the design under real conditions... or just look for some other designer I trust. Later, when you're sailing, if you see that something is coming apart you can always fix it at that time.

OTOH we are all free to heed our concerns and use steel instead of plywood, but the boat might be a tad heavy.

Let me try to get you to give yourself the answer. Think of a sandwich plate and then ask the question where the strength comes from. You will probably come to the conclusion that this is from the deck plates. Of course because the core is in no way strong. If you translate this to your boat, you will see that the wood or the plate is the core and the glass fabric must apply the strength. This means that everything on the inside and outside must be wrapped by glass fabric and epoxy. Ik the building plans on page 7 there you can also see that the fillets should be covered with glass tape. You could also try to glass a piece of stringer totally and compare the strength of it with a piece without the glass. The difference you will notice.

There’s generally no need to build a Wharram stronger than what the plans require. If you plan on keeping the boat for a long time, you should be attentive to protecting against moisture penetration, abrasion, and UV exposure. I’m restoring a 20 year old Pahi that has circumnavigated. There are no problems at all with structural strength of my boat after 40,000 nautical miles. Every issue I am fixing is a direct result of one of those three issues. 

Taping fillets, whether required by the plans or not, is usually a good idea. After taping, you can smooth out the fillet with your finger or a tool and get perfect results every time. Unless otherwise called for in the plans, 4 or 6 oz tape is fine. This isn’t so much about strength—though a taped fillet is stronger. It’s just a good technique for getting a nice looking fillet. I like to cut the tape to length before forming the fillet. Then after shaping the filler, wet out the tape on a piece of scrap wood. Roll it up. Then unroll over the fillet. You can smooth out the thickened epoxy under that tape until it is perfect. 

Filling the weave is a good idea where sanding will be needed (in preparation for paint or varnish, for example). Sanding into the glass bundles will weaken them. It’s also a good idea wherever exposure to moisture is possible, especially down in the bilge. It’s easy to get pinholes resulting from air bubbles or outgassing. Filling the weave helps to ensure that underlying wood is fully sealed. 

Except where indicated in the plans, stringers have plenty of surface area contact with plywood and do not need fillets. Unless required in the plans, no need to sheath on the interior except maybe in a high traffic area where you want extra abrasion protection. 

Maybe we have different plans?
Mine, Tiki 30, Building Plan Book, page 7 is Main Bunks. I can't see or read about any fillet covered with glass tape. It would be nice to talk about the same reality, so, have the plans changed?
About the stringers, you could put a stringer inside a steel tube and fix it there, the difference you will notice.... the added weight you will also notice.


Jozef De Roos said:

Let me try to get you to give yourself the answer. Think of a sandwich plate and then ask the question where the strength comes from. You will probably come to the conclusion that this is from the deck plates. Of course because the core is in no way strong. If you translate this to your boat, you will see that the wood or the plate is the core and the glass fabric must apply the strength. This means that everything on the inside and outside must be wrapped by glass fabric and epoxy. Ik the building plans on page 7 there you can also see that the fillets should be covered with glass tape. You could also try to glass a piece of stringer totally and compare the strength of it with a piece without the glass. The difference you will notice.

yes I am building a tiki 38.

Hello Richard,

I do trust Mr Wharram as a designer! As for the fillets it’s just my prior experience(small boats) and looking at pics of Wharrams and other self built boats seeing the cloth covering the joints, plus that I could only find maybe 36m of the 100meters of glass tape being used. Hence the confusion :)

As for the weave, I get the visible air bubble out and all fibers are transparent. But I‘m maybe am not getting “pinholes".

Thanks

OC



Ricardo Aráoz said:

"So is this overkill or correct?" - IMO it is overkill.Building instructions booklet, Making Epoxy Fillets chapter, paragraph 5, only thing required is "Coat the sanded fillet with epoxy resin to seal it". Then again, you may always build a heavier boat than what the designer intended, the only issue will be you won't be able to carry as much load.

"does the weave need to be filled?" - Building instructions booklet, Coating With Epoxy chapter, Laminating : "you need to fill the weave with the right amount of epoxy and remove all air".

"stringers/stiffeners" - I checked the Building Plan Book and the Building Instructions booklet, as well as the plans, maybe I missed it but I saw not even fillets required for stringers/stiffeners, just glue.

My choice would be to trust the designer unless somebody informed of a concrete and definite failure in the design under real conditions... or just look for some other designer I trust. Later, when you're sailing, if you see that something is coming apart you can always fix it at that time.

OTOH we are all free to heed our concerns and use steel instead of plywood, but the boat might be a tad heavy.

Hello Jozef,

I kinda understand laminates and strength in the outer layers, such as a steel I-Beam(not a laminate but same principle) the top/bottom prevent bend while the web between is just to separate. On my Tiki 30 the ply is the strength and the fiberglass is just a moisture/abrasion barrier. The only place I see a laminate with weak core is in the Cabin Roofs where 4mm skins are used over a foam or balsa core.

In my case I’m covering the below bunk level ply with 4oz cloth as increased moisture barrier and some abrasion protection.

Good idea about testing the use of fillets on stringers. I have been putting 1/2inch fillets on the upper sides of stringers to prevent moisture standing at the stringer/ply joint.

Thanks

OC



Jozef De Roos said:

Let me try to get you to give yourself the answer. Think of a sandwich plate and then ask the question where the strength comes from. You will probably come to the conclusion that this is from the deck plates. Of course because the core is in no way strong. If you translate this to your boat, you will see that the wood or the plate is the core and the glass fabric must apply the strength. This means that everything on the inside and outside must be wrapped by glass fabric and epoxy. Ik the building plans on page 7 there you can also see that the fillets should be covered with glass tape. You could also try to glass a piece of stringer totally and compare the strength of it with a piece without the glass. The difference you will notice.



Robert said:

Hello Robert,

Do you have a website or youtube channel about your Pahi? I would love to see it. What problems are you fixing? You said there were no structure problems. Or….

I also cut the glass out and wet it out on a piece of cardboard covered with plastic. I usually don’t need to do much work on the fillets afterwards, I'm very careful about neatness and am using dollar store spatulas that flex slightly and clean up easily with denatured alcohol to make the fillets.

I hadn’t thought about “pinholes” in the weave, thanks! That’s a good enough reason, especially in the lower areas where condensation or other moisture can accumulate.

Thanks

OC

There’s generally no need to build a Wharram stronger than what the plans require. If you plan on keeping the boat for a long time, you should be attentive to protecting against moisture penetration, abrasion, and UV exposure. I’m restoring a 20 year old Pahi that has circumnavigated. There are no problems at all with structural strength of my boat after 40,000 nautical miles. Every issue I am fixing is a direct result of one of those three issues. 

Taping fillets, whether required by the plans or not, is usually a good idea. After taping, you can smooth out the fillet with your finger or a tool and get perfect results every time. Unless otherwise called for in the plans, 4 or 6 oz tape is fine. This isn’t so much about strength—though a taped fillet is stronger. It’s just a good technique for getting a nice looking fillet. I like to cut the tape to length before forming the fillet. Then after shaping the filler, wet out the tape on a piece of scrap wood. Roll it up. Then unroll over the fillet. You can smooth out the thickened epoxy under that tape until it is perfect. 

Filling the weave is a good idea where sanding will be needed (in preparation for paint or varnish, for example). Sanding into the glass bundles will weaken them. It’s also a good idea wherever exposure to moisture is possible, especially down in the bilge. It’s easy to get pinholes resulting from air bubbles or outgassing. Filling the weave helps to ensure that underlying wood is fully sealed. 

Except where indicated in the plans, stringers have plenty of surface area contact with plywood and do not need fillets. Unless required in the plans, no need to sheath on the interior except maybe in a high traffic area where you want extra abrasion protection. 

Right.

The original poster is NOT building a Tiki 38, he clearly stated he is building a Tiki 30.

Jozef De Roos said:

yes I am building a tiki 38.

That’s interesting that the Tiki38 does show taping fillets while the Tiki 30 does not. Can anybody chime in about other Wharram boats in the same general size e.g. Tiki 31, Tiki 26, or Pahi 31, do their build instructions talk about taping the fillets?

Thanks

OC

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