Stringer re-design advice

[Evinrude Boater]

I'm replacing the stringers and braces in my 16' fiberglass runabout and I'm thinking of re-designing it since I'm not replacing the wood core. The photo shows the only original brace that was in one piece (2x4 material). There were probably 4 or 5 of these on top of a small plywood stringer down the center. There's only about 4" of depth at the center. I was thinking of having 3 continuous stringers running the length of the hull stiffeners (just glassing them in now) and braces between these spaced about 32" apart. I'm also planning to fill the voids with foam. This is a thin hull and is quite flexible as I walk on it. Any opinions on how this re-design will work? Should I pour a higher density floatation foam, say 4lb or 6lb? Will the hull still flex too much in the 32" between the braces? I'm open to all suggestions.<br />

 

[G DANE]

Re: Stringer re-design advice

I have a deep V hull, and it has only crossbraces, for every 12 ". If you jump to the stringer design, the outher stringers will only be maybe 2" high, and I would fear they will break in heavy chop, they will be a little like a stick, but get someone others opinion too.

 

[Sean Riddle]

Re: Stringer re-design advice

Hey Classic, I have the three stringer design in my old Fabuglas (no wood core)and it works fine. The outer stringers are cut down smaller(angle cut) to allow for proper deck height. If you epoxy them in they will be more sturdy than the old ones any day. As for the cross braces nothing wrong with those just be sure to "mousehole" them so water will drain from bilge area and epoxy mouseholed area or entire brace for that fact before installing to be sure epoxy soaks in well in those areas. As for foam you should probably reuse type that was used in original design. You don't want to make her too bouyant. 2lb foam should be all you need then epoxy foam in and she will be solid. Trust me with this new stringer design that baby will be stronger than the original ever thought of being....... Hope this helps, RR

 

[Evinrude Boater]

Re: Stringer re-design advice

Thanks G Dane, I didn't think about the smaller stringers snapping. With the floor on top I thought this would adequately support the small stringers. I would put them directly over the new hull stiffeners. I'm more concerned about the hull between the cross braces. Maybe I should double the number of cross braces. This would cut the spacing down to 16" (400mm). That's normal spacing for floor joists, not that this comparison means anything.<br />Any suggestions on how to support the remaining fiberglass floor at the back of the boat? I'm thinking of laminating a piece of plywood to the underside then sliding braces under that. Then I need to fill the gap below the bilge pit where the wood core was removed.

 

[Evinrude Boater]

Re: Stringer re-design advice

Thanks Riddler,<br />I'm thinking your Fabuglas has a thicker hull if there's no wood core. That's why I'm concerned about re-designing. My common sense says that if I take away the wood core I need to replace it with something else to provide that missing support.<br />The foam I took out was a bit of expanded bead board and some Dow SM. A sure sign that someone else has been working on it. The underside of the bow has a chunk of bead board still attached, who knows what was in the floor. I know I'm not the first to repair the floor. The materials I took out were just terrible, nothing was bonded. Just scooped it out with rubber gloves on.<br />Riddler, do you have photos posted documenting your project? I'd like to see your work progress. Hopefully it'll motivate me. I still have to roll this ol' girl over to do her underside.

 

[Sean Riddle]

Re: Stringer re-design advice

Hey Classic, The hull on my old Fabuglas is really thin too , But when the deck is glassed back in it makes it ridgid as can be. The deck and stringers really make that thin fiberglass strong when everything is back together. I do have a few pics I can share with you

This is what the boat looked like when I got it from my Grandpa (minus old blue gel coating on top of deck). This is the stringer setup with just theh three stringers that run parallel with the hull with no cross braces.

 

[JasonJ]

Re: Stringer re-design advice

If it were me, I would make the stringers out of plywood, maybe run six stringers. You could laminate two 3/4 thick sections per stringer. Sounds like overkill, but that combined with 4lb foam throughout should give you as sturdy of a structure as you would need. <br /><br />The foam would not make it too boyant, it doesn't work that way. The foam is not a boyancy factor until the interior of the boat is flooded, and I assure you, there is not enough volume under that floor to create a possibility of the boat capsizing once swamped. If I were to guess, I would say that there probably is not enough cubic feet of foamable volume under the floor to keep the boat at the surface if swamped, but that all depends on the total weight and water displacement of everything that will be mounted in and to the boat.