Trihull restoration

[Wyoboater75]

Hey guys I'm new here and am attempting my first boat restoration. Lots of learning on the fly. I have 78 Reinell trihull that have I have gutted to the hull.

When I gutted the boat found the stringers and bulkheads were laminated foam. The foam was saturated and the glass was delaminated and split in numerous places. I cut the stringer material out and ground the hull to good glass. Next I layed down a layer of 1.5 oz of csm and a layer of 24 oz roven to built up the hull from having quite so much flex as I had to grind so much out to get to good glass. My plan is to use 3/4 inch plywood for stringers and bulkheads. Would anyone be able to provide some advice if this is acceptable to go from laminated foam stringers to wood? I want to do this resto right so it will last a lifetime.

 

[Scott Danforth]

welcome aboard.

not sure why you would choose to sink thousands into a tri-hull, however its your money.

did you build a cradle to support the boat prior to cutting out everything? if not your boat may no longer be in the proper shape.

go to the sticky at the top of the forum, the one that says DIY links and go thru the links 14, 18, 2, 3, 4a, and 4b in that order. look at every video, picture, etc. in those threads.

all the answers are there.

 

[Hab]

It is going to cost some to get it back into shape, depending on how well you want to re-build it, it can cost alot. Ive read alot of re-builds and the tri-hulls seem fairly straightforward compared to alot of other boat with stepped transoms and multiple bulkheads. as far as your question about wood to replace foam, im a novice as well and dont have a ton of experience, but I believe that there is no structural value to the form material (foam has no bending strength and wood will get wet and rot). You will get all your structural integrity from the fiberglass that you wrap the form material in. So foam, wood, legos, cardboard, or osb could be used to reform the stringers. Again Im not a boat designer and that is only my opinion.

 

[Redtruck12]

I’m gonna disagree on the stringers.
Material matters and although there are some designs that use foam and other materials that is an entirely different design with different engineering properties.
you need the structural strength of a stringer. They are definitely more than forms to shape the fibreglass.
ever heard of anyone using foam insulation board to shape stringers..... I haven’t.
if it had wood - replacement with wood!
read the how to sticky’s, they will explain the right way to do it

 

[Redtruck12]

It is going to cost some to get it back into shape, depending on how well you want to re-build it, it can cost alot. Ive read alot of re-builds and the tri-hulls seem fairly straightforward compared to alot of other boat with stepped transoms and multiple bulkheads. as far as your question about wood to replace foam, im a novice as well and dont have a ton of experience, but I believe that there is no structural value to the form material (foam has no bending strength and wood will get wet and rot). You will get all your structural integrity from the fiberglass that you wrap the form material in. So foam, wood, legos, cardboard, or osb could be used to reform the stringers. Again Im not a boat designer and that is only my opinion.

Not sound advice IMO

OSB? Cardboard? LEGO???????

I personally would never even consider any of them.
i read a recent post in another thread about what appeared to be old “fence boards “
cross those off the list too.
Anyone who has never “been there” needs to educate themselves through research and thought out question
whats your experience Hab???

 

[sphelps]

From the first post Wyoboater said the original stringers were glassed over foam . Which is not uncommon.. Just needs the right layup of glass for strength .The glass Was probably comprised and then the foam got saturated. A good freeze may have caused the delamination . It May add a little extra weight but I see no problem with going back with plywood if you want ... IMO and I am not professional by any means ..

 

[Hab]

I’m gonna disagree on the stringers.
Material matters and although there are some designs that use foam and other materials that is an entirely different design with different engineering properties.
you need the structural strength of a stringer. They are definitely more than forms to shape the fibreglass.
ever heard of anyone using foam insulation board to shape stringers..... I haven’t.
if it had wood - replacement with wood!
read the how to sticky’s, they will explain the right way to do it

I would really appreciate an engineering perspective on stringer construction. What is the purpose of the stringer? Is it adding strength to hull, or does it merely support the deck?

I stand by my opinion that an optimum stringer material weighs very little, does not change the flexibility or rigidity of the fiberglass encapsulating it, and does not deteriorate in water or hold water. IIRCC i have read where one pro has advocated for hollow stringers, but its been awhile.

Its also my opinion that the main reason for working on the stringers is to remove the saturated form material. After grinding my own out, i wished i had only cut the top 1/2" off, dug out the remaining mulch, scuffed up the exterior and glassed em back over, hollow.

 

[Wyoboater75]

Thank you for the constructive advice. I'd like to go back with plywood then tab it in to the hull. I just haven't been able to find any information to find if this is acceptable. I understand that this cost to do this resto is considerable but the boat itself holds tremendous value to myself. I've watched and followed all of Friscoboaters Searay videos I like how he went about his rebuild. It maybe overkill for my trihull but but there's no kill like overkill

 

[Hab]

Here is a good read on the stringer material question.

https://forums.iboats.com/forum/boa...lternative-products-for-stringers#post9947307

Im not advocating for a bunch of nonsense materials, but I did want to point out that most of us are not engineers and trying to figure out how much of each material is equivalent to the original strength is difficult at best. Replacing foam with ply should be stronger and you will benefit from the additional strength of the wood. I am replacing dimensional lumber stringers with plywood, and several more layers of glass than the single layer of roving that mine were covered in. I'm also hoping that the additional stiffness of the stringers doesn't adversely affect the rest of my hull and crack the remaining glass since I will be reducing flexibility to some extent. Again my opinions only, for what its worth.

 

[Wyoboater75]

I think at this point I've decided to go with 4 stringers of 3/4 inch plywood with bulkheads between all the stringers. As originally it only had 2 foam stringers this should add considerable structure. My next question is there a point where stiffening the hull is bad? Or is it merely trying to balance stiffness and weight?

 

[chevymaher]

Just balancing stiffness and weight. There are jetboats with metal hulls. They run out of the water channels racing. They just flip them over and stick them back in the water. Keep on racing them. No way you will reach that level of stiffness.

 

[Wyoboater75]

[No message]

 

[Wyoboater75]

Finally seeing progress after so long!!

 

[Woodonglass]

I'm not a Nautical Engineer, but the stringer material debate was a HOT TOPIC several years back here on the forum. We HAD several PRO's make comments about it and the general consensus was..The Glass encapsulation is what bears the majority of the stress but...ONLY if it's adequately thick. Most of them stated that 1/4" minimum thickness was required if you wanted to use foam or a HOLLOW stringer design. That's why wood is used as the core material for most less expensive boats. The wood gives added longitudinal strength and aids in keeping the flex of the hull to a minimum. To get 1/4" thick fiberglass walls on a stringer would require approximately 4-6 layers of 1708 biaxial fabric and resin. It's really not economically feasible to do this but if you consider the costs of composite materials it might be something to consider.

 

[mickyryan]

the other choice is seacast by making stringers then pouring in , works great as well sea cast or arjay 6011

 

[Scott Danforth]

I am not a naval architech, however I know many of them, and for work reasons, I get to visit many boat builders

just an example.....Malibu and Ski Nautique stringer tubs are almost as thick as their hull. same as Chris Craft.

higher end runabouts and wake boats as well as others do not use traditional stringers anymore, however engineered stringers, all pulled as modules from plugs and molds and all glued together in the hull with plexus

However there is some significant tooling capitol spent after a significant amount of engineering goes into the hull and stringer tubs.

many low-volume boats today still use encapsulated wood or foam with traditional layout or bagging methods. however as WOG stated, they use a large amount of resin and biax.

 

[Hab]

Progress looks good Wyo.