Refinishing Hull

Thanks ondarvr , I am just wondering about how they distinguish strength. Am I right that 3 layers of 6 oz cloth would be equal to 18 oz matt even though the thickness is different. I am not familiar with the terminology on the bottom of the boat but there is an area on the boat that I don't like the thickness on either side . It is the area that would run horizontal to the water . There are 2 of these areas on each side of the boat. I feel it is not thick enough to my liking seems to be thinner then the rest of the boat. This area had alot of chopstrand running the length of the boat on these surfaces . They are in from the outside chine maybe they call them the second and third chine then the keel or something to do with planing surface. I was thinking of adding a couple or 3 layers of 6 oz cloth from stern to bow along these areas . Just throwing some ideas around in my head.

 

What you are describing sounds like lifting strakes, which run fore and aft and are typically wedge shaped from side to side if fitted on the bottom and just a flattish longitudinal area along the chine, if at the edge of the bottom panels.

If you think it needs some material, then add some and no, 18 ounce mat is not the same strength and stiffness as 3 layers of 6 ounce cloth. Technically, it's not a fair comparison, because the polyester and mat has different physical properties than epoxy and cloth. The epoxy and cloth will be stronger, but slightly more flexible, assuming better resin to fiber ratios in the epoxy laminate, compared to the polyesters typically low fiber to resin ratio.

 

I am just waiting for the temps to rise we are still below freezing at nights here but looking like end of next week we are going to break the 55 temps. I just don't want a curing issue to arise because of the temps and my stove quit or something .

After reading your reply you have the areas described and I made a mistake on the comparison . I meant to say comparing 18 oz roving strength to 3 layers of 6 oz cloth strength. Should the 6 oz cloth have to be built up to the same thickness as 18 oz to be comparable. I can't see it being comparable at 3 layers but am just wondering just to give me an idea of how strengths really work. I read at different forums people comparing and adding up weights of material and say the weights are the same so the strength is there . They don't talk about thickness. I would think thickness would count. I know mat does not have much structural at all.

Sorry if I am waisting anyones time asking these type of questions but I would just like to learn a little about strengths.

Sorry about the comparison my mistake on types and Thanks again for the reply Par

 

Having the same amount of glass in weight doesn't mean the laminate will have the same properties, sometimes it can be close, but in testing you typically see differences. This doesn't mean one is better than other, it depends on the properties needed for the stresses the part will see in use. Turn one of the 6 oz layers of cloth at 45* to the other two and the properties change.

Like PAR said, if you think an area is too thin then add a layer or two, worst case you spent a little money and made it a pound or two heavier.

 

Great advice as usual. What would be a good mixing ratio for some putty that is more structural for building up before fairing. I was thinking maybe 1:1 ratio by volume for epoxy resin to cabasol and then maybe 25% of milled fibers. Does that sound about right or is there a better ratio.

Thanks

 

Cabosil is a good filler, though I'd recommend a 50/50 mix or even more milled fibers, with your application. In the industry, we call milled fibers "liquid 'glass", because of the looks once mixed and it's usual applications.

 

Ok just a little update and a couple questions. I mixed up my structural mixture about 1 oz resin to 1 oz cabosil to 1oz milled fiber. I am finding with my mixture it is very thick after mixing it up . After I use it for 10 minutes it almost goes back to a mayonaise mixture and will begin to sag. I am thinking the kick off of the epoxy is thinning it out. What is your trick should I let the putty sit for 5 minutes and add some more filler to keep it at thicker consitency. Would you add more cabosil or milled fiber.

Another thing is if I decide to run some cloth to replace the layup layer over the complete hull bottom to the water line after I get the initial bruises fixed and faired.

What Weight of cloth would you recommend?
Just one layer. I am thinking I should add something as I found a few hair line cracks running for and aft in the bow of the boat just in the lay up layer. From front of stringer out about 15 inches. This could have been caused by weak stringers but I replaced them all last winter or the design of the hull. The deck over the ski locker was not tabbed to the hull in the bow . All boats i have seen around here the deck is tabbed the whole perimeter, so I will tab mine in when I flip it back over , which will support the bow a little better.

If i decide to layer the boat with cloth to replace the layup layer would I just do like 3-4 layers of epoxy on top of the cloth and call it my barrier coat then do my final fairing from there.

When I started this project last year I said I was going to do it right and I don't care how long it takes as this boat is going to be mourned just off the back yard of the summer home for me and my wife to enjoy an evening cruise across the arm when we retire.

 

Any Suggestions Thanks

 

You mix fillers for the need, not necessarily by volume or weight. Environmental conditions will also play a factor as to how much of what you'll use.

If you mix a batch of thickened goo and leave it in a mixing cup, pooled in a mass, it'll kick off before you have time to spread it around. If you spread out the thickened mixture, into a thin sheet on a piece of flat something or other (I use bits of thin plywood that have been previously sealed with straight epoxy), then the exotherm reaction is greatly reduced and you can get a much longer working time from the batch.

As to what weight cloth to use, well a single layer of cloth will not make it much stronger, unless you use a really heavy fabric. Cracks should be fixed (ground out and filled) before fabric goes over them.

If your mixture is sagging, you've not got enough silica in it. A mayonnaise consistency will sag, every time. A non-sagging mix will be like peanut butter. Silica is the key to non-sagging mixtures. It's a thixotropic agent, used to control viscosity.

It would be wise to download the user's guides from westsystem.com and systemthree.com, so you can read up on techniques and methods.

 

I have been reading the guides and doing lot's of reading and watching alot of videos . What I found was the stress cracks were just in the glecoat and the chopstrand . Not very big about a ft long and maybe three of four together. Once I cleaned off the chopstrand the stress cracks are gone. Flex cracks is what they look like to me.

I am not really looking for much strength as everyone says chopstrand has none. The chopstrand was more like 1/16 of an inch in most places but thicker in other areas .

I was thinking of running a layer of cloth just to seal the bruises I have fixed here and there( cutting out layers of laminate etc) beaching bruises etc. Make it one complete layer on the bottom. Watching some old timers videos they have been sealing their plywood boat bottoms with a layer of 4 oz after doing the initial fairing etc before final fairing.

I just feel the chopstrand had some strength too it . Old style fiberglass gelcoat tubs are not that thick and are all chopstrand and hold up some pretty big people .

If I was looking for strength what weight of cloth would you recommend.



Thanks Par

 

stress crack are telling you a story ! read and understand what its saying !!

Stress cracks are a sign of a weakness and a panel /corner flexing or what ever !! Its a sign telling you something is wrong If you don't strengthen then it will keep repeating the same thing all over again !!
Find the weakness and do something about it !!
If you insist on using light glass cloths then look at the direction of the cracks and lay the glass strand across where the cracks were ,do more than just one layer and turn the next layer 45 Degrees so the glass strands are holding and distributing stress loads into a bigger area then finish off with a layer or two of sacrificial chopped strand matt .

 

Gelcoat is brittle...Flex it and it cracks. Are these cracks dangerous ? Dont know...most times they are only cosmetic.

To fix them you must stiffen the panel or if they are the result of stress concentration..spread the stress. When you add a stiff structure onto a flexible hull you will get stress cracks.

If you are worried about the cracks, contact a surveyor or NA and have them take a closer look.

 

Exactly !!! Thanks for the advice . That is my initial repair I have removed the chopstrand ( the stress crack do not go beyond that, I checked with a back light and glasses) and am going to replaced it with a couple layers of cloth. I am using epoxy so mat a no go. What I was getting at is I removed the chopstrand from the entire hull up to the water line and was wondering what I could use to give the boat a layer or 2 or something in replace of the chopstrand .

thanks again

 

Micheal , that is not my concern and am not worried about the cracks. I was just trying to figure out what I could use to strengthen up the hull where I removed all the chopstrand. One guys preaches to remove it and don't worry about it but I was just inquiring what people use in replace of chopstrand. I know they replace fiberglass on bigger hulls after using a planer and have to add more material. I just don't know what to use for cloth if I decide to replace it.

thanks

 

If the hull is flexing the re-strengthening needs to take place inside the hull and only a small amount outside !!
The hull panels are bending inwards across the hard points like where bulkheads and stringers and internal framing will be placed directly to the hulls skin !! this will be a major job for sure !,some stiffening can be done from outside but depends on what glass you use !!
Things like double bias 45/45 would be my choice as a starting point with a second layer of 0/90 (not woven roving )over the top !.
OR a triaxle 90/45/45 also with a 0/90 as the second layer on the outside !!

Something to take note of is when you have stiffened the hull bottom of the boat it will ride noticeably harder and could pound a little more than before !! Remember now the internal framing will be stressed much more than before ,so cracking could shift from the outside skin to the inside frame work and beyond like deck joins and corners

Gel coat cracking is also related to the gel coat thickness !! Gel coat forms like an egg shell, so the thicker it is the more it will crack and the bigger and deeper the cracks will be!!
The thinner the gel coat the less cracks and much smaller and only shallow !!.
For high speed boats cracking allows water to get in under high pressure and gradually works to flake off the gel along the stressed area and even start to penetrate the fibreglass as it to will be weakened from the continual bending and flexing a thousand times a hour !!
DO YOU HAVE ANY PICTURES YOU CAN POST ??