Stringer Grinding help needed

[IHTFP]

Hi,

I am currently in the middle of a complete stringer and transom replacement on a 22 Ft powerboat. I have removed all the wood from the stringers but have left the glass tabbing that encapsulate the wood about 1 inch high from the inside of the hull. Is this acceptable, or should I grind the tabbing down until it is flush with the hull? I thought I would leave the 1 inch of tabbing, which would help me locate the new stingers properly and will keep the hull stiff while the stringers are under repair.

Thanks

[rickr]

This is how I am doing it. It is my first experience with fiberglass work.
Link
http://www.boatdesign.net/forums/fiberglass-composite-boat-building/ski-boat-stringer-sole-replacement-20668.html

[IHTFP]

Rick,

Thanks Rick. Nice project.

Any other comments out there, is it better to grind all the way down to the hull or leave a tab ?

Thanks

[Landlubber]

IHTFP,

It would be normal to comletely remove the old and reinstall the new, just take pics and measurements before removal and they will go back roughly where they were, no big deal if they are a thou either side of the original....

[IHTFP]

Thanks,

That makes sense to completely grind them out. Both ways make sense to me, which is why I am asking those who are experienced.

Thanks

[naturewaterboy]

Why are you removing the fiberglass? The wood probably does not contribute to the strength, it is usually only a mold material.

[Landlubber]

natureboy,

It restores the rebuild to as per standard by tidying up as you go...that is all

[IHTFP]

Thanks,

Are there any special precautions I need to take to make sure the hull doesn't lose shape once I grind all the tabbing out? The hull is well supported on a bunk trailer.

[naturewaterboy]

I wouldn't remove the glass. The strength is all in the glass. You really didn't need to remove any of the glass, so leave what you have and just rebuild the stringers. If you grind them all the way out, the boat may twist. It may twist anyhow. Before you start adding back stringers, I'd say you should be very careful to support the boat very well and very level and straight. If you twist the hull any, you'll have a boat that won't run straight without a lot of extra drag, and it may even be dangerous. Just my non professional 2 cents.

[LMB]

Heres a few effective suggestions that are reasonable compromise. I would double check that the hull is evenly supported at as many points as possible. Naturally stiff areas like the keel and chine are the best areas to support the boat. Support between stringers could be a problem. I would not make any major adjustments unless you discover a potential problem. I usually level a boat left to right and front to back and then use a 5' carpenters level to take some measurements from the keel to the chine, comparing each side working from the transom forward. Tolerances are most critical at the stern. That may be hard to do on a trailer. Now I would work on one stringer at a time. Cut/grind the inside edge tabbing down flush. This would be the side closest to the keel. Use the remaining upright tab to align and bond in the new stringer. Cut the stringer bottom on an angle to closely match the bottom of the boat. This will minimize the gap to fill. To bond in the new stringer use a reinforced resin putty to fill gaps (including between old tab and new stringer) and spread to a nice filet along the open edge. The hull to stringer joint is the most critical area. If you have large gaps to fill you might need to pack in some chop strand mat, as too much putty can be a problem. Then glass up the sides of the stringer. Proper prep and clean air pocket free glass work is very important, so grind down any rough spots as you go. Plan each lay-up in manageable portions, remember you have limited working time with the resin. I would glass up each side leaving the tops to be planned level with the other stringers. Once everything is level you can glass over the tops.

[PAR]

Why remove material that you don't have to. You have enough work to do.

The original tabbing is great at locating the new material, helps hold it in place as you bond things and helps save on the amount of additional material you have to install.

Grind down the tabs so they have a dramatic taper to them, so the new tabbing will "bulk" and grip over a large area.

Bed the new stringers in well soaked mat, which will provide a good bond if using polyester. If using epoxy, then use a thickened mixture of resin and skip the mat, in favor of cloth (you don't need mat with epoxy). Extend the new to old tabbing out into the hull shell, so the new stuff can insure a good grip. This is a little over kill, but a lot of folks do it. It's likely the old tabbing is enough to get the loads transferred to the hull shell.

As has been mentioned, support the hull so it doesn't distort as you move around inside or under it's own weight. Most trailers don't offer enough of this support. It doesn't have to be level, but it helps, especially when putting in stringers, seat boxes, etc.

Log onto www.WestSystem.com and download their user's guide to work with epoxy. It covers the techniques you'll be using, assuming you'll be working with epoxy.