Foam or no foam? That is the question.

[Fatlenny]

Newer member here and starting to get to work on the winter project, a 79 Checkmate Jetmate2. This is the first boat of this type I have owned. I am a little familiar with restoring boats as last winter I completed a 14' Glastron clone project. (well I guess the project is never really done as I plan on doing a splash well delete on it in the spring next year) Well on to my interest in advice on what path I will take and the education I will need.

I am learning a lot about Jetboats over the end of the summer and this fall but have a lot more to learn as I am getting ready to get to work on this winters project. As I was talking to another jetboat owner I learned what a quarter stringer and a full stringer boat is. This 79 Jetmate2 is a quarter stringer. The Floor is rotted and foam water logged. I started the removal and clean up of the old flooring and foam. I found that under the floor it had a 3/4" plywood stringer imbedded in the foam that I assume was for supporting the floor. this was not glassed into the hull. (I dont know if this is original to the boat or was redone at sometime) The throttle cable was imbedded in the foam. (was this how it was done from factory?) Talking to one of the guys at a Michigan Hot Boating meet, He suggested removing the floor all together, that it was not needed for this hull. I can see the reason for this thought from someone who only wants to "go fast" as this is a great weight reduction. He also added if I was to put a floor in it, to not use any pour foam. Lastly as for the condition of the rest of the wood in this project, at this time it appears the transom is still very solid along with the quarter stringers. Time will tell as I am unsure if I will pull the motor for this project this winter at this time. My plans for this boat is to use it mostly as a family fun boat to pull the grand kids on the tubes, but have a little extra performance to be a little silly on the water when I feel the urge. I plan on keeping a floor so the family has a flat surface to stand on while moving around the boat.

Questions/advise:
1. Does this 79 have a balsa core that needs to be inspected and possibly replaced? (I dont look forward to doing this work but believe I can do it with a little research)
2a. Is the foam necessary to add stiffness to the hull and better support the floor on this 79 Jetmate2?
2b. If answer is no for 2a. I plan to use some 3/4 materials to recreate the 3/4 rotted plywood with some cross pieces added to support the floor. Can I just embed these "stringers/floor supports" in 5200 or do I need to embed them and tab them in with fiberglass?

 

[karzrus]

Pretty sure all checkmates have balsa core in the hull bottom, sides and top deck to add thickness to the layup for stiffness. I know my 82 Eluder did.
also pretty sure foam was only for floatation, but there was some side benefit like stiffness /support.
If you are going to all this effort why wouldn’t you treat/coat any wood you add with resin and fully glass it in after bedding it with 5200?
or are you planning to replace the wood with composite or plastic material, still would glass that in place.

 

[Fatlenny]

I am planning on replacing the rotted 3/4 plywood "stringer" with something other than wood, but haven't decided what materials yet. I say stringer loosely as it was not tabbed in, It only looks like it was set in place with a small amount of some kind of caulking material. I feel no soft spots so far on the bottom of the hull, and wonder how I can tell if it has a balsa core. The cap of the boat is not balsa core as I can see some light trying to get through it from underneath. Just occurred to me that maybe I can take a high powered light and see if it shines through the bottom of the hull to tell if the bottom is Balsa. I think I would rather not use foam again as over time it becomes waterlogged and there is nothing that can be done about that. But if the foam is not only for floatation and gives some structural support to the bottom of the hull, well then I feel I must.