When is fiberglass done for?

If the mast and associated gear is workable you already have half a boat.

I cant believe that the hulls are dead. Its possible the the highly stressed mechanical joint that connect the hull to the cross braces needs attention.

If the hulls were foam filled this foam added to the stiffness of the hulls...put it back after you have cleaned up the inside of the hulls

I doubt that you need to add any interior structure. If the hull bottom is chafed on centre line , then a good grind and a layer of triaxial eglass tape down the center from bow to stern ,set in epoxy , would be a sensible repair that also adds stiffness fore and aft.

Ibelieve that the survey for a catamaran is to assemble the cat, block it up, then physically twist the boat to see how much the hulls deflect. Cats. like to have both hulls going in the same direction when sailing

Ask a cat guy for a better description for the flex test

 

I'd agree, though without seeing it, this is a guess, it's unlikely the 'glass is shot. Most boats are driven hard enough for long enough to kill the 'glass.

As to loyalty to West System, this is great and several of the employees and the founders are friends, but when you can buy the same quality, blush free products from someone else and less then 1/2 the West System price, it's tough to be loyal.

I think you may be over thinking this set of repairs. As Michael mentioned, stop by the local sailing club and find an experienced multi skipper to have a look. This may or may not be helpful, but you can ask enough questions to find out if he has a clue, just by what you've learned from the Gougeon brothers book on boat building.

Hard points and attachment points will likely need addressing (more reinforcement) and the abrasion areas, additional fabrics, but I think this is about it for your boat. You can "over kill" these areas without too much of a weight penalty and have a stiff, stout boat.

 

http://www.boatdesign.net/gallery/showphoto.php?photo=23168

http://www.boatdesign.net/gallery/showphoto.php?photo=23167

http://www.boatdesign.net/gallery/showphoto.php?photo=23170

http://www.boatdesign.net/gallery/showphoto.php?photo=23171

http://www.boatdesign.net/gallery/showphoto.php?photo=23172

http://www.boatdesign.net/gallery/showphoto.php?photo=23169

Well here are some photos of the Prindle. (if they work) Based on what everyone has written and my recent observations I do think it would be relatively easy and cheap to rehab except for the sails. With my long winded post earlier what I should have more concisely asked. What is a good reference to quantify the strength and stiffness of various fabrics, cores, bulk heads etc. I know there has to be an engineer who gather the data for a reference source for small boat builders and rehabbers. I know what can add strength, and stiffness but I don't know when it is just plain over engineering. Thanks Justin

 

I don't think that worked. I posted the link in the pop up window for each photo in my boat design gallery.

 

Let me see if this works

 

Now I tried adding some through manage attachments.

 

Well now we are getting somewhere.

 

Looks ok to me. Heavily fatigued fiberglass shows a spiders web looking crack formation on the surface gel coat. The glass fiber flexs but the brittle gelcoat cant so it cracks. Investigate any of these spider web areas. Make sure the bottom has not been chafed and worn thin by dragging it over the beach.

 

I see a few things I'd address before splashing, but the 'glass looks okay. The plywood on the inside of the transoms doesn't appear to have much resin on it, check for rot. If it's okay, apply a healthy coating of resin to seal it up.

Again reinforce areas you think needs it and the best route is epoxy and biax, though you could do it with poly, mat and roving - it'll just weigh more. These little bits of here and there reinforcement will not hurt much. Scale, structural replacements/reinforcement and laminate thicknesses to be similar to what's there. As to engineering guidelines, well most engineering is application specific, so engineers try to avoid generalities. Odds are, you only need to fix a few cracks, gouges and worn areas, find a set of sails and have fun.

 

Michael- thanks for the description of bad fiberglass. That is some of what I want to know.

Par in regards to engineering I am not asking for generalities. I am asking for some material science specifics and some structural engineering specifics. Panels of triaxial, biaxial, woven and mat of similar weights or thicknesses has been tested. Core material, and stringer shape, size and location has been tested. Somebodies got data. I am not talking cargo ships, or tug boats but sail and motor boats under 40 feet. Naval architects are not making it up as they go along. The evolution of boat building and material science has come a long way and someone has attempted to quantify and qualify that somewhere. Is there a reference book that most people in the industry utilize? There are similar text in any other construction industry. I understand that boat designers don't want some novice adding crap here or there but not all boats are built well, designed well, or utilized for designers intended purpose. Justin

 

If you are asking about engineering in general, there are all kinds of books about marine engineering and people can advise on those. One I always hear about is "Geer's" something or other.

But as far as engineering boat repairs, you generally don't engineer small repairs, you mainly try and replace what was there using good work practices. If the boat is much heavier when you're done, you've probably over engineered.

 

As I mentioned in the previous post and Sam has reinforced, just fix what you have, with a similar laminate schedule. if you employ better materials and resin, the same thickness laminate will be stronger, for the same weight. If you see areas where you think you might need more reinforcement, bulk them up, knowing better techniques and materials compared to what the manufacture used will likely carry you through.

Yes, there's lots of data, but it's also dependent on your understanding of measurement systems, terminology, physics, chemistry and engineering principles. If you want you can absorb a whole bunch of data and information about stuff you'll rarely if ever need, or you can just fix you boat and get her wet.

If you want a general guide, you can get Dave Geer's book "Elements of Boat Strength" which will offer more information then you ever wanted about laminates, applications, etc., though it will not explain the engineering behind them, just offer "robust" solutions for specific applications. Bring your calculator when you get this book, as you'll need it frequently.

 

This has made me think about the following: how is it possible to know the laminate schedule of a hull when completed?. No wonder the thickness, which is useless, but by the various layers of the laminate.

 

When you grind back old, damaged laminate, it becomes pretty obvious how thick it is and the schedule is also usually visible. In a production build, you can bet there'll be alternating units of mat and roving, so figuring the replacement schedule is fairly simple. If not, you can just bulk it up to the same level, saving any head scratching, math and frustration.

 

If schedule is visible is because work has become very bad. Normally it is not visible. On the other hand, the switch mats and rovings without further can result in a very wrong composition. When there is no alternative, such as the usual case, filled with whatever it is and go. But this is a major problem and so I wanted to know if anyone had a technically correct solution. I see that so far, no.