1989 BFN Rebuild

I am in the middle of a complete rebuild of a 1989 BFN with 454. When I bought the boat I knew it had motor problems (water had gotten in cylinders). Turns out it had slipped a rod bearing, but was otherwise okay. Rebuilt the motor and had the transmission overhauled as well. Just I was about to put the motor back in I notice some real soft spots up by driver seat. I knew that meant stringers and foam (I had been reading tons on CCF from all you guys). So rather than put the motor back in an worry about it, I bit the proverbial bullet and cut into the floor. I found exactly what you would expect - wet foam and rotting wood stringers.

Well that's how I got here! My plan is to do a composite rebuild using Coosa Bluewater 26 and use polyester resin rather than epoxy (seems like overkill and a lot extra expense from everything i have read plus it helps justify the cost of the Coosa). At most I would only like to foam in the front section back through the drivers seat.

What I am trying to work out now is how to best layout the stringers and supports w/o foam. You will notice in the pictures below that the 89 BFN had the following:
- Main stringer - made from a 2x4 and is 10'-6.5" long. The Engine cradle rest on these.
- Secondary stringer - Probably made from a 1x10 as it is 8.5" at it tallest point. It is 13'-10.5" long.
- Third stringer - Could have been made from 1x6 stock. It was pretty much destroyed and came out in pieces, so I haven't measured this.

I would like to use Coosa 1/2" x 3 layers to build the mains. For the Secondaries I could use Coosa 3/4" but from other builds I have seen here the secondaries were eliminated in favor of cross member support (re Another BFN Rebuild). How important is the third stringer (which I haven't seen in any other rebuilds or pictures)? Should I just duplicate what is there and replace and put in a coosa floor for stability? Would love to hear your recommendations...

Finally - one more question. How is the ski pole in front of the engine laid in? Can I just cut it out? (I broke the bolt off trying to get it out. I drilled the bolt out but was still unable to extract the Pole. Figure if I can get it out on the bench it will easier to repair...)

Cheers - Mike

Boat when I bought it.

I think oil might be a better choice to run in here...

This is when I found the soft floor

First reveal after floor removed...

Here you can see all three stringers

Rear View before the foam removed

Here is where I am as of today...

That 3rd set of stringers is a new one to me- there was no such thing in our 79. I haven't seen anything of the sort in any of the other bfn rebuilds either. Are you saying there were no ribs and bulkheads to speak of? That is strange, they seem to do a fine job of keeping the v-hull in the shape of a vee. It seems strange for cc to have switched construction techniques so late in the boats run (90 was the last year). I wonder if the boat had been restrung previously?

If you've never worked with the different types of fiberglass before, I'd highly recommend epoxy. Not only is it stronger and less apt to absorb water, it's also a lot easier to work with. That alone is worth the extra cost on a project this scale. The cost shouldn't be appreciably higher- check US Composites for materials.

Oh, and a '89 would have been built with vinyl resin (ame4000) not poly- so I'd use that as a minimum. I'm not sure if poly will stick to vinyl... I know it doesn't stick to epoxy. Epoxy sticks to everything.

Thanks for the responses! I am a newbie at this boat building stuff but have always loved correct craft and just couldn't let a potential gem like this one get by with out some serious care and attention!

3rd Stringer - From everything I can tell this was all original and the first time the floor has been up. No ribs - just long stringers and foam. I am leaning toward just recreating the stringers as in the pictures and covering with 1/2" Coosa - maybe 3/4" under the front area. Seems like this would be easier than custom building/fitting the the ribs in aft sections.

Epoxy vs Poly - I really hate to spend the extra bucks but you make a good case - particularly with respect to ease of use. I have done a little fiberglass work but may moons ago. Quite a different product selection these days.

HDU - Very interesting. Will it take a lag screw like wood? That could be a real bonus. Any idea how it compares price wise to Coosa (1/2" is $265 for 4x8 sheet)?   

SNobsessed wrote: There is an even more important reason to use epoxy - The factory resin was epoxy ('89 was the 1st year for this) so polyester wouldn't bond well to the base material.

That definitely sold me!! Though my pocket book is crying :(
The knowledge on this forum sure goes deep - thanks that could have been a big mistake...

Thanks I did read it and plan to go back and review it some more. I find if I do some work on the boat and then go back to re-read sections,I get a better understanding. Do you know what year his boat was? I am looking around for info/pictures closer to year model .

I found one thread on here for a 1989 ski Nautique rebuild. Its stringer configuration is not the same as I found in this 89 BFN which had a 3rd set of stringers. Can anyone confirm if this is factory correct?

Also I am still trying to get the center pylon out. I was able to slip the engine cradle up and off but twisted the bolt off that holds it in the cup base. How is the base installed? Is it just glassed in and can I grind it out to remove?

Thanks - Mike

Ski Oz wrote: HDU - Very interesting. Will it take a lag screw like wood? That could be a real bonus. Any idea how it compares price wise to Coosa (1/2" is $265 for 4x8 sheet)?

Mike, You got me thinking on bolting straight into HDU so tried it out on a off cut (2 bonded together) we use here....Spec is a fine grain 15lb HDU 2’inch thick which I lag bolted (4in) up through a steel plate into the edge of one layer of the off cut around centre with a strap hanging 119lb off it....no pilot hole just wound it straight in with a wrench.
My thoughts, yes you can screw into HDU coarse thread needed....can strip/over tighten 4’inch lag bolt @ around 15lb in the sense that it just turns with the HDU rides over the threads not stripping out like metal.
If I were to use on a stringer project would go for 30lb + if using HDU to lag into only....wood screws also work well into HDU with coarse threads and would use longer screws/lags than in a wood project.
There are more test results on the link... under technical with west system bonding.
As for cost you will need to call a HDU supplier in the US as we have lots of shipping costs in the UK.

TRBenj wrote: Roger, it looks like HDU is available in greater densities (up to 75 lb/ft3)... Which one did you run your test on? Coosa is only available in a few, primarily 20 and 26 lb/ft3 (the latter being the choice for stringers). Other than that, I see that both products are closed cell foam based (urethane/polyurethane). Coosa has layers of roving and strand glass built in- I see no mention of that on the HDU. Just curious what makes you think it's a better material, as I don't see anything obvious.

Tim, As I said in my post above the off cut I used is fine grain 15 lb on test...you are right to point out all Coosa is a HDU with glass on each side (not sure if there weights are with or without glass)but for many Coosa is not readily available around the world, HDU is and as you will be adding glass over it you can fine tune the Core (HDU) to suit their needs/application, over cost availability in the US or around the world, it’s just another option to play with.
Better or not will always be down to execution/spec but more important there are more than one way to go.

Ski Oz wrote: SNobsessed wrote: There is an even more important reason to use epoxy - The factory resin was epoxy ('89 was the 1st year for this) so polyester wouldn't bond well to the base material. That definitely sold me!! Though my pocket book is crying :( The knowledge on this forum sure goes deep - thanks that could have been a big mistake...

TRBenj wrote: Oh, and a '89 would have been built with vinyl resin (ame4000) not poly- so I'd use that as a minimum. I'm not sure if poly will stick to vinyl... I know it doesn't stick to epoxy. Epoxy sticks to everything.

If your hull sides don't have cracking then I wouldn't be worried about changing that stringer layout. I was swayed towards epoxy for its superior adhesion, not that stronger is needed, but it will compenste for rookie craftsmanship! I'm rebuilding the same hull and will not copy the many bulkhead design either. Look at any walk through Sport. Substantial v-hull up front, ski locker (no solid floor) and lastly no deck providing support either.

TRBenj wrote: 4. Set up an account with Composites One and a 4x8 sheet of 1/2" b26 should be <$200

I have a supplier here in West Palm but his price is around $265 for 1/2" (in stock) and $525 for 1-1/2" (all 4x8 sheets). I noticed Composites One has a distribution branch in Miami - about an hour and 15min drive for me. Definitely worth it if one can save 25%.

To your point about the ribs: I am still thinking it through but with out the foam in the aft sections I will need something to replace that support. Maybe not as many ribs as you did but at least enough to add support and hold the floor. One bulkhead just forward of the engine and maybe one about halfway back to where the hoses turn up - let the foam do the rest...

btw - Do you sleep? I saw a post at 4:20am!

Mike

I have been spending quite a bit of time working on revising the stringer design while I grind and grind and grind... Not to mention this is the worst time to work outside here in florida as it hot and very humid! The following is some CAD work I have been doing.

Cool exploded view. If I ever have to do my stringers, I'm gonna give you a buzz.

JPASS wrote: Cool exploded view. If I ever have to do my stringers, I'm gonna give you a buzz.

I have to give cudos to TRBenj. He did it originally in his BFN rebuild. It sure helps when you want to lay things out...

[Knew there had to a reason...it's definitely waterproof and bouyant though!

I keep debating with myself about the foam... On one hand I want to avoid any possibility of rot yet if I do a good (careful) job and use the better c!osed cell foam I should have minimal issues. I figure I will pass the boat to my grandkids (13 & 8) one day and it might save them...

Probably do the foam.

Thanks that was driving me crazy trying to figure that out. I guess if I were more of a fisherman I would know that.

Lots more work but I have to agree with earlier comments that it will be much better when done with bulkheads and ribs. At my age (61) I likely won't ever do this again!