Stringer and Bulkhead Repair - 1970s Baja SS16

[Henni]

I'm replacing the stringer, front bulkhead, and possibly some marine foam in the floor of an old 1970s Baja speed boat (best guess is model SS16, year 1976-1978). I've attached a photo of the boat as I'm not 100% sure of the model or year.

Does anyone have design plans or photos of what the structural stringers and bulkheads are supposed to look like for this boat (or a similar model). The previous owner replaced the floor and I'm not sure if what I'm looking at is reflective of the original design of the boat (see photos below). He may have removed some foam, bulkheads, and definitely redesigned the ski-bar attachment. With these changes, I'm unclear on the 1) way the deck floor (plywood) is supposed to be attached to the inner-hull fiberglass floor running up and down the sides, 2) whether there is supposed to be more bulkheads, 3) how the ski bar attachment support was originally constructed, and 3) length of hull lined with foam.

I've removed the floor and removed the rotten front bulkhead (3/4' plywood), and plan to remove the single center stringer, as it is also rotten. I also removed foam (looks to be about 2 lbs/cuft) that was strongly adhered to the stringer and hull. The foam only seemed to be installed under the floor deck 1/3 of the way from the front bulkhead (under steering wheel) toward the back of the boat, but I'm not sure if it originally covered the entire stringer length back to the bilge area.

Regardless whether someone can provide original design plans for this boat, I'm looking for advice on how to reconstruct the structural support for this boat. I plan to replace the front bulkhead and centre stringer, but I’m unclear on what to do from that point on. The main questions I have are: 1) is it better to reinstall the foam along stringer and V-hull under floor, or instead install additional bulkheads every 3-4 feet down the length of the hull, or both; 2) how should I reattach the inner-hull fiberglass floor that runs along the sides to the center plywood floor (not shown) – should I epoxy this inner-hull fiberglass floor to plywood floor AND to the main hull (i.e., should I join the hulls)?

I'm a newbie, so bare with my ignorance please.

Thanks,
Chris

 

[Henni]

Here is another link I found to a similar boat being restored. https://www.kijiji.ca/v-powerboat-motorboat/muskoka/16-ft-baja-ss/1463383160?undefined.

 

[Henni]

The HIN for my boat is ZTH151130176 if that helps.

 

[GA_Boater]

The HIN decodes to a 1976 Thundercraft.

 

[Henni]

OK, must be the wrong HIN, sorry. And cool to see how easy it would have been to look that up myself. Now I know. Thanks.

 

[GA_Boater]

What does the paperwork say? Any state issued documents should have the builder's name.

 

[Scott Danforth]

without paperwork its a yard-planter model

 

[Henni]

Paper work gives the wrong HIN (I guess). Can't quite make out the serial number in the fiberglass anymore, and it was a guess for the previous owner too, so the paperwork is probably wrong. I'm up in New Brunswick, Canada.

Any recommendations on whether I should put foam back in when I replace the stringers?

Thanks

 

[Buckischloo]

You should definitely put the foam back in. I have 1973 V1600 I am rebuilding. Mine had the foam just in the front like yours. I figure they put in just enough to keep it legal but no more to keep it cheap. I am going to fill ours with foam front to back to give the floor and the hull support. Mine had just the one stringer down the middle. It also had a box like structure in front. I will try to add a picture of a Checkmate that is identical to how our Baja is laid out once I learn how to add pictures.

Paperwork can be tricky. Being in Ohio they tell me that if I get it inspected by the DNR, they will give me a new HIN tag. This 1973 did not have a HIN molded in the hull. Motors without paper work are a no go.

 

[Chris1956]

That boat is build a lot like my '74 Avenger. On my boat, the decking stops about 1 foot from the gunwale, and that 1 foot is just heavy fiberglass. The center of the hull is 1/2 plywood decking over stringers and foam. I have 5 stringers, versus your 3.

If it were me, I would add 2 stringers between your outer ones. There looks to be a spot where the originals might have been. I would use dry pressure treated solid lumber, and glass them all in, waterproofing them. If the existing stringers are in good shape, simply reglass them to the hull.

The front of the hull needs a triangle-shaped piece of solid pressure treated lumber to seal the front part of the decking. That chunk of foam in the bow was open to the air. Make sure it is still not water-logged.

The rear of the decking should extend to the transom. The stringers should be foamed with 2 part pour-in foam,and trimmed to eliminate any air. The decking should be dry pressure treated plywood, screwed to the stringers with SS fasteners. One or two layers of glass cloth and resin will seal the deck. I fiberglassed 2X2 PT lumber to hold the seats, versus using screws to attach them. Much stronger than screws and no leaks into decking.


As for your ski bar support. My old seaRay had SS bolts glassed in under the decking to support the seats. You could do something similar. Take some 5/16", 3/8" or 1/2" stainless bolts with large washers and place them on that heavy fiberglass. Some strong aluminum plates are better than large washers. Anyway, glass the bolts + washers/plates to the heavy fiberglass part of the hull, perhaps with some 1/2" plywood and glass to fill the entire height of the decking. Let the bolts stick up enough to bolt the ski bar to them.

One more thing. The original foam in your boat probably wouldn't float it, if it were to swamp. I would replace as much of it as I could. If you have space under the gunwales for foam, that would be a good idea as well.

Best of luck.

 

[kcassells]

Yup...agree with Chris.

 

[Henni]

Following advice from others above (thanks), I’ll plan to reinstall the foam under the floor (1/2 ply) from the ski-bar to front bulk head. The foam upfront looks in good shape, so I will leave that as is.

I plan to add a ½ inch drain pipe from the front bulkhead compartment, under the new floor foam, to the bilge area, and add a vent in the front bulkhead to allow air to move around in there. This pipe will also allow drainage of that compartment should the need arise.

Once the new Bulkhead, stringer, and foam is replaced, I’ll install the floor with a ½ inch piece of plywood encapsulated with glass/resin, and then bond that floor ply to the stringer, floor and inner hull, front bulkhead, and I’ll make sure the floor contacts the transom with two ply knees in order to make sure I get good force transfer from transom to the floor and stringer.

My progress on the stringer bulkhead has stalled for now though, as the Transom is also shot, and I’m going to start there. If I’m going to do all this work, no point in only half fixing. I could dig through parts of the Transom with my bare hand! I’ve attached some photos. It took me about 20 hours to dig that transom out, which also required cutting the splash-well and sub-floor a bit to make room for the new transom layup. See photos.

I plan to use two ¾ inch pieces of Coosa Bluewater 26 board for the transom, and I’ll have enough Coosa in one 4X8 sheet to also use it for the stringer and bulkhead.

I’ll be working on this project for the next 4 months, so any more advise on any of this would be much appreciated. This is my first time doing any of this work.

Thanks

 

[Davetowz]

Looking forward to watching you build. Always remember to budget at least twice the money and 4 times the time as you initially think it will take. BTDT. Keep building!

 

[Henni]

I managed to glue in the new transom and bulkhead this weekend.


String, floor, and, splash-well repairs up next. I'm still on the fence with the 2 part pour foam under the floor. I’ve read a lot of posts about this going wrong (cracked hulls, incorrect temperature leading to open-cell foam, and lack of drainage once in). I like the structural support idea of the foam, but also want limber holes (drainage) under the floor, and it is tricky to have both. Unless I pour the foam into a plastic lined boat, remove it, and cut a drain path, it will be tough to achieve continuous drainage from the bulkhead to the bilge area, so any more advice on this would be appreciated.

 

[Scott Danforth]

foaming on plastic, then pulling it out defeats the structural aspect of foam

do a good job encapsulating and then maintaining and you dont need limber holes and drain holes

seal all the wood stringers properly
install sole with pour holes for foam
foam it and go boating.

you are thinking too much about it.

 

[mickyryan]

If water doesn't penetrate the foam areas and freeze the foam will never go bad, i just learned this about a boston whaler that never had foam issues even though water could get to it , it never absorbed it because it had never frozen and cracked the foam, upnorth water penetrationnand freezing is what makes the foam a soggy mess id imagineor if foam had ever gotten frozen with water in it

 

[Chris1956]

I vote for the pour in foam. Your hull is probably strong enough without the foam, but you will want the flotation for safety.

I also agree that drainage under the deck is not necessary. Seal her up. It is the best way. I recommend a medium weight fiberglass mat over the decking plywood. I had cracks develop in the resin and cloth, when I used medium cloth. Heavier fiberglass material is likely better.

I would also make sure to use some heavy mat or roving, on the edges of the transom, where the transom meets the hull. overlap the transom by 4" and the hull by about 8". You will want good strength there.

What is that grey coating on the plywood? Hopefully you are using only resin and cloth on the plywood. Anything else is unnecessary and could cause an issue with bonding.

BTW - the pictures show an A-1 repair job.

 

[racerone]

You mention a ----" double hull "----Is that balsa cored in those areas ?-----Balsa core was used as it is light and makes a stronger assembly.------Only untll the balsa gets water logged and rots away.