1972 Keel Up Restoration

I have studies Mark Bano's restoration pics extensively. I am going to go a slightly different route. No Wood. Someone told me on this thread that the factory put the balsa core into the shell hull and then put the stringers in on top of the core. That to me is just wrong. After i install a new transom I plan to put the stringers in and tie them to the transom and hull directly. Transom and stringers will be laminated 1/2" Coosa Bluewater 26 composite to a thickness of 1 and 1/2". I will support the shell hull by any means necessary to keep the proper shape to avoid hooks or any other hull problems. I will continue to support the hull when I install the Divinycell core between the 3 stringers and possibly some to the outside of the outer stringers. I am not sure what thickness I should buy the Divinycell core foam at.

I have also decided that the best way to support the skeg and ski pole is with plywood if my kitchen cutting board idea does not work out. As much as I am against wood in the lower hull of a boat it would be only be a small amount of wood and in the 2 places it would be would not be a water collector and totally enclosed with fiberglass. I do not plan on using any expandable foam to fill in "areas" like Mark did but I plan on designing the water dranage to allow any water that may make it to the core top to drain unimpeded to the stern. Likewise for the floor (which will be installed after the deck is re-installed to maintain proper hull shape).

Another thing I am going to do is make the motor well wider to accept twins. I plan on installing transom knees that double as motor well sides. Those knees will probably be too wide apart to extend or tie in to the outer stringers but no problem - the more knees that attach to the transom the stromger the boat will be. I want a bullet proof transom for big HP motors.

What I am attempting to do is take a classic boat and turn it into something you could buy today that is modern in construction and materials. I think I can do this for under $10K and where can you buy a new boat these days for less than $15K?

A couple of questions:

1 - What thickness of Divinycell foam should I use for the core?

2 - When I install the stringers and transom should I "tab" them in with fiberglass tape? I just bought a lot of fiberglass tape. Another website says to do that but fiberglass cloth does not do 90 degree corners well. I am assuming small pieces of resin impregnated cloth is what they mean to just secure the stringer or transom to the hull until one is ready with bigger pieces of resin impregnated cloth to tie it in as described below.

3 - They say put fairing compond in to make a nice curve. I figgure fairing compound is like Bondo. For the stringers I could also use fiberglass filler to attach it to the hull shell but that stuff is a bitch to sand but certainly better than fairing compound for strength.

3 - Mark Bano used cross-stringers to replace what he found. I found no cross stringers in my boat. I understand cross stringers will make a stronger boat but are they really neccessary if I do as I have outlined above?

As always all suggestions are appreciated. In the future I hope to put this restoration project up for all to see like Mark Bano did.

 

If you study Ab Crosby's and Ab Crosby Jr's writings and talk to them, (they designed these boats) they will tell you that the strength of the hull is in the core, not the stringers. The balsa core acts as one big stringer distributing the loads evenly through out the compound curve structure. The design has proven itself
through years of rough ski team service. Try and find some stringer boats that have lasted this long. They are not there!!!

If the transom load paths are to the bottom through the stringers it will tend to put rocker in the bottom. The transom loads in the Dyne are carried by the hull and deck structure itself which in essence give you a stringer that is the total depth of the hull.

Some of the really high end boats use end grain balsa core, which when properly installed will not allow water to propagate through it.

By the way, on one of my first boats, I dug 1000 pounds of soaked closed cell foam out of it with a shovel.

I talked to a ski team that bought a new inboard with no wood in it a few years ago. It picked up 300 pounds of water the first season.

jim

 

Jim you about have me convinced to core the bottom with balsa and then add stringers as the original design did. I think the main reason my core(s) rotted out was water leaking in from the skeg and nowhere to go. Perhaps I can isolate the skeg area with composite materials and balsa core around that area.

 

Actually you could get a new 17.6 dyna-ski for around $10k. Don't have the current prices.

 

I have often thought that you could glass a sleeve into the transom mounting bolt holes to help seal them. I think you could glass in a sleeve for the skeg mounting bolts depending on whether you choose to use a bolt or lag screw. There are some pretty good sealers out there too.

By the way, I have no issue with composite stringers and floor as long as you can glass in something to mount the pylon and seats to. Allison bass boats have a composite/metal transom.

If you do the end grain balsa, do a little reading on how it is installed. For instance, each section is dipped in resin to seal it before installation. I think they use epoxy for that. Polyester is not water proof unless it is gel coated.

jim

 

I think I am going to use Divinycell for the core with stringers over it like the original design. There will be an area with no core above the skeg - I am going to wall that in so if the skeg does leak again it will be confined to a very small area. If my kitchen cutting board idea works I will install that board in the walled off area and then glass over it and the divinycell surrounding the walled in area thus sealing the skeg area in. If the cutting board material proves unuseable due to non-adhesion with resin I will use plywood. I intend to thru-bolt the skeg using SS hardware and lots of sealent such as silicone unless someone else has a better idea.

I am going nuts just talking about it and not working on it but I am also learning alot from you guys and appreciate it. Do it right or do it again...

 

If you decide to use the Divinycell, I would try to find it with sufficient density to have the same or better shear strength as the balcore. Since the core acts as a beam the core itself will see some shear stresses although most of the load will be carried by the hull and floor. Any failure in shear will destroy the strength of the hull. I would also install it with the same procedure as they install the balsa. i.e., seal each piece and bond the pieces together and bond them to the hull and floor.

jim

 

For a sealant below the waterline, I would not use silicone based products. 3M makes two products including 4000 or 5000 (slow cure) and 4200 or 5200 (fast cure) marine sealant that are very resistant to photodegradation and are specifically designed for this task. I was told by the guys that replaced my transom on the HD 20 i/o to use the 4000 series because the 5000 searies can tear off the gelcoat if you ever have to reseal for any reason. used the 4000 slow cure for my through-hull bolts for the ski deck on the referenced boat and it worked great. Kind of scary drilling through $2,800 worth of repair work but after this stuff sets up, it forms a exceptional bond and flexible gasket.

just my $0.02,

Kevin-

 

Got the sealent 3M 4000 idea. I will use that. I am a regular paricipant on the screamandfly.com forum and also get alot of info there. That is a very large forum so more advice. Don't get me wrong - this forum is a total gem for Hydrodyne stuff. And thanks Jim for your advice. BTW Jim what part of Florida do you live in? Next weekend I hope to pick up 7 sheets of 1/2" Bluewater 26 and install a 1/2" transom and work on the skeg area.

 

I live in central FL.

I am a member of S&F, but I sold my hot boat so I don't go there any more.

1/2 inch sound like a very thin transom. Most skiboats are much thicker to properly transfer the loads.

jim