building engineered stringers!

[55evinrude]

Hello everyone! I might be getting a rotten 16' ski boat soon and im pricing out the cost to rebuild it and I have just been thinking about making engineered stringers. Yes i know wood last years if properly fiberglassed but i'm just looking to do something different for the hell of it!

Anyways i was thinking of building a plywood forum and pouring that 2 part foam in it so that way its very strong foam and in the shape I need. I was wondering if that would work? and if theres is something i can spray on the plywood forum before i pour the foam so it doesn't stick (like the stuff they spray in a boat mold before the gelcoat!). so if someone would let me know if making a foam stringer would work, also i would obviously being fiberglass wrapping it but not sure how many layers it would take. another concern is if it would be strong enough (of course my big four winns has factory installed engineered stringers so they must be able to be made strong)!

Nathan

 

[jigngrub]

Re: building engineered stringers!

Why not just cut and bed in some sheet foam stringers?

 

[55evinrude]

Re: building engineered stringers!

Why not just cut and bed in some sheet foam stringers?

I thought about that! I just figured the pour foam is pretty strong especially if you pour it in a tight space aka a form!

Nathan

 

[jigngrub]

Re: building engineered stringers!

Ok, but it's a form, not a forum.

... and here's some mold release agents to put on the plywood to keep the foam from sticking:

Mold Releases

 

[55evinrude]

Re: building engineered stringers!

Ok, but it's a form, not a forum.

... and here's some mold release agents to put on the plywood to keep the foam from sticking:

Mold Releases

lol woops I was putting forum instead of "form" my mistake :facepalm:

Thanks for the link jigngrub!

Nathan

 

[tpenfield]

Re: building engineered stringers!

Yes, I agree with JNG . . . take some polyurethane foam sheets and make your stringer/bulkhead layup, just as you would using wood. Then glass over it to bed them to the hull and make sure to glass over the sides and tops with several (or more) layers of fiberglass.

I see no need to make an elaborate mold for a 16 foot boat. A traditional approach using foam sheets instead of plywood sheets should do the trick. The only difference is that you will be relying on the fiberglass covering of the stringers for all of the strength.

 

[Woodonglass]

Re: building engineered stringers!

You do realize that it will take a minimum of 4-6 layers of CSM and 1808 Biaxial Cloth to yield a Foam Filled stringer strong enough to deal with the forces placed upon the hull. Basically the walls of the stringer need to be at least 1/4" thick and you cannot have any bubbles in the layup. That's why they're called engineered Stringers. If you are wanting to do this so you don't have to replace them just remember that properly laminated wood core stringers will last 40+ years if you properly maintain and care for your boat.

 

[55evinrude]

Re: building engineered stringers!

Thanks for the input guys! I think your right about just using foam sheets, And I do realize that this will cost a lot in fiberglass but I think it would be worth it. I will have to refresh my glassing skills so I don't get air bubbles but I am up for the challenge :happy:. The only reason I want to do this over wood is just for the challenge and just something different,even though my last boat a 1976 Doral was slipped its whole life and never had any rot so that shows how well wood can last! thanks again guys!

Nathan

 

[1FASTLASER]

Re: building engineered stringers!

Why not just cut and bed in some sheet foam stringers?

this sheet foam you speak of can you post a link as to where to get it?

 

[jigngrub]

Re: building engineered stringers!

this sheet foam you speak of can you post a link as to where to get it?

It's the XPS (extruded polystyrene) rigid foam insulation board sold at Home Depot and Lowes:

Foamular 1/2 in. x 48 in. x 96 in. Squared Edge Insulating Sheathing-36L at The Home Depot

You can buy it in varying sheet sizes and thicknesses.

 

[tpenfield]

Re: building engineered stringers!

It's the XPS (extruded polystyrene) rigid foam insulation board sold at Home Depot and Lowes:

Foamular 1/2 in. x 48 in. x 96 in. Squared Edge Insulating Sheathing-36L at The Home Depot

You can buy it in varying sheet sizes and thicknesses.

Polystyrene sheets are not the best thing to use as the polyester resin will eat the foam. (sorry)

I did use polystyrene to build my custom anchor locker in my F-242, but it was an uphill battle trying to isolate the foam from the resin. Link: Fiber Glassing . . . The resin eats the foam for lunch.

You could go with epoxy resin . . . or just give the cut foam an epoxy coating to protect it.

Vinyl Ester resin won't be any better than the polyester resin . . . here is a link to a thread about that: http://forums.iboats.com/boat-resto...am-vinyl-ester-compatability-test-407267.html

Polyurethane foam sheets will be more pricey, but will be compatible with the resin . . . they are sold more as an industrial product, so you will want to Google your way to some suppliers, etc.

The benefit to using polyurethane foam will be that the fiberglass will have some adhesion to the foam, thus getting some dimensional stability, etc.

 

[jigngrub]

Re: building engineered stringers!

My bad for not realizing/mentioning the volatility of the poly resin and poly foam, but if I was going to build engineered stringers I'd rather use epoxy than poly for strength and ease of application/use (no respirator).

 

[Woodonglass]

Re: building engineered stringers!

The resin will also EAT the polysheets from Lowe's Easy and cheap way to avoid this is to wrap it with Packing Tape. There's no need to worry about the glass adhereing to the core. The glass is what does all the load bearing. If Wood Stringers had 1/4" of glass encapsulating them then you could let it rot away and never worry about it. If you proceed with this it's critical that you grind the hull glass and get a really good bond with the overlapping layers since the glass WILL be the structural component to keep the hull in shape. Waves and wakes take a heavy toll on hull and stringers.

 

[55evinrude]

Re: building engineered stringers!

Thanks a bunch guys for all the info! Wood: good idea about the packing tape :eyebrows:. If I get the boat I will have a big decision to make of whether or not to go this rout. generally how wide should I make a glass stringer? the same width as a wood one? Just wondering for pricing and such! Thanks

Nathan

 

[55evinrude]

Re: building engineered stringers!

just seen something on the internet: Plascore Board - Marine Board - Plascore Board Panels

What if I used this for the transom floor and stringer core? and I just looked at other boats like this one and they only have 1 center stringer :happy: so thats less work to do!

Nathan

 

[Woodonglass]

Re: building engineered stringers!

Stringers are a VITAL component of your hulls overall seaworthiness. It's usually NOT a good idea to change the configuration of their design. The Engineers that designed the layout for them had very good reasons for doing it that way. The plascore is VERY exensive but is very good stuff. If you use it, I'd recommend staying with the original design and use plascore instead of wood. Engineered stringers most of the time are a minimum of 4" wide. the tops usually have a 1x4 piece of wood glassed on top in order for the deck and seats to be attached.

 

[jigngrub]

Re: building engineered stringers!

just seen something on the internet: Plascore Board - Marine Board - Plascore Board Panels

That stuff looks interesting, but where can you get it and how much does it cost?... I looked and couldn't find a distributor or prices.

 

[55evinrude]

Re: building engineered stringers!

Stringers are a VITAL component of your hulls overall seaworthiness. It's usually NOT a good idea to change the configuration of their design. The Engineers that designed the layout for them had very good reasons for doing it that way. The plascore is VERY exensive but is very good stuff. If you use it, I'd recommend staying with the original design and use plascore instead of wood. Engineered stringers most of the time are a minimum of 4" wide. the tops usually have a 1x4 piece of wood glassed on top in order for the deck and seats to be attached.

I realize that stringers are important, I will be rebuilding the boat exactly the way it comes apart with whatever materials I use. The boat only has one center stringer to begin with so overall thats pretty simple lol! Thanks for the info on stringer width thats a big help. I am also looking at coosa board for the deck but its soooooo expensive :faint:

Nathan

 

[55evinrude]

Re: building engineered stringers!

That stuff looks interesting, but where can you get it and how much does it cost?... I looked and couldn't find a distributor or prices.

yeah thats the one issue is price and distributor, I will have to look in to it more!

Nathan

 

[jigngrub]

Re: building engineered stringers!

yeah thats the one issue is price and distributor, I will have to look in to it more!

Nathan

I'd like to examine and test a piece of that stuff because I'm skeptical about the durability of it... and if it's not as strong as wood and costs more than wood I don't really see the practicality of it.