Hard spots on hull (bedding question)

[rickryder]

I am a little confused on the bedding and hard spots theory. I have read about not placing stringers directly on the hull because it will cause hard spots. To remedy that you bed the stringer in PB or PL.... Ok what is the difference if the hull is fiberglass and the PB is fiberglass chop strands,cabosol and resin wouldn't that be the same? PB and Pl will dry to a hard substance against the hull.... Please help clear this up in my brain well what left of it anyway!

 

[Yacht Dr.]

Re: Hard spots on hull (bedding question)

There is no/little difference between directly laying the stringer to the hull .. or .. filling floating stringers with PB IMO.

True floating stringers are just that..floating off of the hull ( 1/4"ish ).

I have in past posts recommended both ways. However depending on the size of boat and size of open pan areas you can get away with either.

YD.

 

[sasto]

Re: Hard spots on hull (bedding question)

PB is my choice. There is a thread about plywood with or without voids. Why are voids acceptable in the layup of a stringer and not in the wood used? Personally, no void for me. Stringers do little in preventing flexing and twisting of hulls, bulkheads do most of the work.

A long debate amongst boatbuilders. Good Luck. rickryder

 

[Cadwelder]

Re: Hard spots on hull (bedding question)

PB is my choice. There is a thread about plywood with or without voids. Why are voids acceptable in the layup of a stringer and not in the wood used? Personally, no void for me. Stringers do little in preventing flexing and twisting of hulls, bulkheads do most of the work.

A long debate amongst boatbuilders. Good Luck. rickryder

I too have asked this question on this forums and from other builders...I lay my stringers in a PB mix right agaisnt the hull. I've restored boats that were built both ways. Also brings up the fillet questions again 90% of the restores I've torn down had no fillets anywhere. (All I've done are under 21'). I've never run fillets up until now and my current restore now has them....don't know if it helps alot or not.....makes a better layup that's for sure.

 

[Yacht Dr.]

Re: Hard spots on hull (bedding question)

PB is my choice. There is a thread about plywood with or without voids. Why are voids acceptable in the layup of a stringer and not in the wood used? Personally, no void for me. Stringers do little in preventing flexing and twisting of hulls, bulkheads do most of the work.

A long debate amongst boatbuilders. Good Luck. rickryder

Its not only stringers that should float..its the bulks too.

I have repaired many of hulls/bottoms because the ply was directly on the glass.

Bringing the stringer or bulkhead right up to the hull will not improve the bond..that would be the fiberglass' job .

The surface area of the tabbings ( lets say 5-6" on each side of the wood ) distribute the energy across the hull Way more then 3/4" of wood.

Its like taking 3/4" x 6" stringer..put that upright..and start banging with a sledge.
Take that same 3/4" x 6" and lay that flat and start banging away ..

Which one is going to cause more damage to the hull ? .

There are other factors .. but this is a basic idea.

YD.

 

[sasto]

Re: Hard spots on hull (bedding question)

I too have asked this question on this forums and from other builders...I lay my stringers in a PB mix right agaisnt the hull. I've restored boats that were built both ways. Also brings up the fillet questions again 90% of the restores I've torn down had no fillets anywhere. (All I've done are under 21'). I've never run fillets up until now and my current restore now has them....don't know if it helps alot or not.....makes a better layup that's for sure.

You have a point, Cadwelder. Especially on size. I've never built anything under 30 feet and all were very rigid hulls. We always used fillets, and I would assume this procedure would also aid in spreading out a hard spot.

 

[sasto]

Re: Hard spots on hull (bedding question)

I have repaired many of hulls/bottoms because the ply was directly on the glass.

Bringing the stringer or bulkhead right up to the hull will not improve the bond..that would be the fiberglass' job .

YD.

Not being a repairman, but a builder, I have never expierenced hull failure due to hard bonding of stringers. Our methods involved in having no voids anywhere in the lay-up schedule, whether it be a stringer or a bubble.

I have seen your work and it is very professional. I have also noticed most are sailboats. Is there a difference between them and a powerboat, YD?

 

[Cadwelder]

Re: Hard spots on hull (bedding question)

You have a point, Cadwelder. Especially on size. I've never built anything under 30 feet and all were very rigid hulls. We always used fillets, and I would assume this procedure would also aid in spreading out a hard spot.

Yep to the size....all my restores are on "production boats" Ondarvr responed to my question about the fillets with it's a time and cost issue in the smaller crafts.....the manufactuer doesn't want to spend the extra time required for the fillets and the "perfect fits" and these boats seem to be fine as far as strength and lifespan.

The Astro I'm rebuilding right now had some hugh air bubbles in the tabbing and bridged gaps on the stringers and yet it lasted 17 years with no problems. True it had a lot of rotten wood (hence the restore) but who can say how much longer it would have held up with no work to it at all.

 

[Yacht Dr.]

Re: Hard spots on hull (bedding question)

Not being a repairman, but a builder, I have never expierenced hull failure due to hard bonding of stringers. Our methods involved in having no voids anywhere in the lay-up schedule, whether it be a stringer or a bubble.

I have seen your work and it is very professional. I have also noticed most are sailboats. Is there a difference between them and a powerboat, YD?

You notice sailboats mostly..because those are the pictures that I have posted . I have worked/repaired/built on each just about the same.

I dont see many hard point cracks on sailboats..mostly power boats. Skipping across the water on plane does seem to create more energy than sliding through it.

I didnt mean to say hardbonds will fail the hull..but it could start cracking it.

You can filit..but I would not use structural putty. I would use microballons or some othere kind of fairing compound.

YD.

 

[rickryder]

Re: Hard spots on hull (bedding question)

I thank you all for your replys! Great info and I will bed my stringers in PB and filet so I have a nicer job in the end. Now I understand the theory of spreading the load to the hull better. Thanks again guys!

 

[oops!]

Re: Hard spots on hull (bedding question)

hard spots on the hull....where the stringer meets the hull......will cause gellcoat cracking, or crazing,
using pb, is different because fiberglass flexes.
i wish i had more time with this......but i have a bazillion pm's to do and little time to do them.

 

[ondarvr]

Re: Hard spots on hull (bedding question)

There is another factor or reason in spacing the ply off the hull and its compounded in larger hulls due to size of scale.

When Resin cures it can shrink a great deal, the better stronger resins tend to shrink a little more. So when the ply touches the hull and is glassed over the shrink of the resin will drive the ply even more solidly against the hull, which will pre-stress it even before it ever sees the water. As the stringer becomes larger, the shrink increases resulting in more stress. Typically on small boats the glass over the stringer isn't enough to overload the hull, this has to do with the hull normally being thicker than it needs to be to resist the stress, plus the resin used doesn't shrink as much.

 

[Cadwelder]

Re: Hard spots on hull (bedding question)

There is another factor or reason in spacing the ply off the hull and its compounded in larger hulls due to size of scale.

When Resin cures it can shrink a great deal, the better stronger resins tend to shrink a little more. So when the ply touches the hull and is glassed over the shrink of the resin will drive the ply even more solidly against the hull, which will pre-stress it even before it ever sees the water. As the stringer becomes larger, the shrink increases resulting in more stress. Typically on small boats the glass over the stringer isn't enough to overload the hull, this has to do with the hull normally being thicker than it needs to be to resist the stress, plus the resin used doesn't shrink as much.

So you're saying don't bed them(stringers) anywhere with anything? Set them in and glass them in with a slight gap and just bridge the gap with the glass? Or better yet bridge the gap with a fillet and then glass over them....I'm a little confused there?

 

[ondarvr]

Re: Hard spots on hull (bedding question)

No, I'm just adding info on what can happen if the plywood is touching the hull. The gap can be filled with whatever you like, its not going to make a huge difference.

 

[Cadwelder]

Re: Hard spots on hull (bedding question)

Okay, just wanted to clear there.....I've always beded them with a PB mix and will continue then. As you know running the fillets is a new addition for me, but will continue that too. Thanks.

 

[GracieBell1]

Re: Hard spots on hull (bedding question)

I have been following this thread as it hits home for me, as does RickRyders. I have the Liberator. From the facotry I have a gap of about 1/4. Four Winns said it and the wood in the motor mounts and bulks should be spaced off of the hull. Four Winns used the glass tabbing to bridge tha gap. Ondarvr is the man!!!The glass actualy shrunk inward, under the stringer. I hate floating everything because this is where the rot started. When I told Four WInns that I wanted to bed everything, encapsulate the stringers and use scarf joints with scabing on one side, he said I was building a tank....If I float could I use expanding foam to fill all of the gaps, or just bed in PL premium since it will flex? Thanks for your wisdom...

 

[Yacht Dr.]

Re: Hard spots on hull (bedding question)

The glass actualy shrunk inward, under the stringer.

Just not possible..

I dont know what your question is..but you might start another thread ( If you havent allready ) ..

YD.

 

[GracieBell1]

Re: Hard spots on hull (bedding question)

well for whatever reason the glass pulled
under the floating stringer

 

[barbosam]

Re: Hard spots on hull (bedding question)

There are many methods to float stringers, one method that no one has mentioned is to use a high density closed cell foam between the plywood and the hull. This foam is expensive and maybe not practical for your average back yard builder. This is often done on stiffeners for production molds for pretty much all the same reasons everyone here has already listed. Basically anything that can fill the void, not absorb water, not rot and is softer than the plywood itself will work to float the stringers.

 

[barbosam]

Re: Hard spots on hull (bedding question)

I should also mention that any material you use to float the stringers should be tested for compatbility with the resin you are using. Most often its epoxy resin which should be compatible with just about anything but poly or vinyl ester resins can react with certain materials (ex.= styrofoam).