Glassing in an old thru hull hole.
- Thread starter kito
- Start date
Ron20324;
You are not privy to what I have heard or seen over the years and that sir is one tidbit that many do not think of which from a former dealer perspective I experienced. There are those who think otherwise without thinking of pressures and no I am not GEICO. I am human just like you.
You are not privy to what I have heard or seen over the years and that sir is one tidbit that many do not think of which from a former dealer perspective I experienced. There are those who think otherwise without thinking of pressures and no I am not GEICO. I am human just like you.
I think Ron was just adding some levity to this otherwise intense and serious topic
Interesting. Just did a rough estimate on my boat and came up with about 4 psi on my hull sitting still. Not unless my math is wrong. Wetted area in square inches divided by displacement?
4 psi would put the hole about 8 feet under water. The bond strength of polyester resin is greater than 400psi.
The bonding area is tapered about 12x the hull thickness at a minimum so the quarter inch thick hull with a half inch hole would get a patch about 7 inches across or roughly 50 square inches x 400 psi bond strength.
The bonding area is tapered about 12x the hull thickness at a minimum so the quarter inch thick hull with a half inch hole would get a patch about 7 inches across or roughly 50 square inches x 400 psi bond strength.
On a larger hole, could one also place a circle of marine plywood as reinforcement and then glass over in both inside and out? I was thinking that with a thicker hull it'd take forever to fill the hole with just glass.
What many of you do not see behind the scenes is what boat yards experience and see. z I have seen a lot in my life time. There are some folks who attempt repairs without the knowledge what they are doing. Twice, minimal pressure as it may be forced the private repairs of holes in two boats that sunk as a result because I had to bring those two boats up where the angled repairs were from the outside to the inside, thus the larger portion of the hole was inside. I also dealt where the angle was just the opposite, angled outward from the inside with the larger being on the outside and several times those repairs were leaking but did not push out toward the inside. Those boats were pulled and repaired before they sank.
Many on this forum know what your are doing but then again there are those who do not and at times I reach out to those folks too, thus the reasoning behind methods of repairs I do.
You can fault me for what I believe in but understand I have experienced more than nearly all of you in many ways during my lifetime.
Many on this forum know what your are doing but then again there are those who do not and at times I reach out to those folks too, thus the reasoning behind methods of repairs I do.
You can fault me for what I believe in but understand I have experienced more than nearly all of you in many ways during my lifetime.
DO NOT TRY any short cuts the repair should be at least as strong as the rest of the hull. I don't need to hear people being impatient with hull repairs. I laid 2 full rolls of chopped strand matt and one roll of 24 ounce woven roving in a hundred gallons of resin when I re-fitted Bietzpadin. This is just one little hole in a hull. do it right and proper.
I'd use G10 instead of plywood. The WEST site talks about putting a plug in the center of the hole then glassing in on both sides using a 12 to 1 taper. Ross is right on with his pressure, Scuba divers use 33 feet depth for each atmosphere. So air pressure at the surface is 14.7 and at 33 feet it is 29.4, then at 66 feet it is 44.1 and so on. You can extrapolate the pressure versus depth since this is linear.
The hole most be backed in some manner or you end up with a bulge on the non working side. The easiest way is a barely large enough path over the hole and allowed to cure and then fill from there. Whenever possible is best to work both sides with equal care and attention to detail.
I have no room on the inside to do any beveling since I have a seacock close by. I was going to lay 1 or 2 layers 1808 flat on the inside and let harden and build up from only the outside. Sometimes I wish they would just make blank thru hull fittings to plug unused holes. That way it could be used later if needed. This is a hole that an old paddlewheel transducer was in.
Using a hard piece of stock as a filler would be a very bad idea no matter what material you were to chose. The reason for grinding out a 12 to 1 bevel is to gain greater greater surface area but maybe more importantly is to spread the load so there is no hard spot. The patch needs to have the same flex or lack there of as the rest of the hull. Do not use a wood or glass plug unless you also bevel that to the same standards as the original hole. Then you would have to cut donuts to fill the thing. You get the idea. No square holes or sharp lines. Everything needs to blend very smoothly to retain the original strength, Steve.
A 12 /1 scarf is a min and 18 -20/ 1 better. That is the thickness of the original times the scarf. The patching material to be used should be as close to the original layup as poss. Grinding is best done w/ 36 grit and as flat as poss. First layer should be the largest one and sould be chopped strand mat usually 1 1/2 oz. Only a couple of layers put down, let set up, then next and so on. Wet out material on a flat table using a paint roller and use lots of pressure. Shoot for about 1 lb of material (w/ natural glass) to 3/4 lb of resin. Then place on part (first paint the part w/ resin)and roll it out. Large patches can be fan folded on table. This leaves the exsess on the table not the part. This has been tested as best by military and manufactures. Promotors in resins have been used by most boat builders to decrease cure time. These make secondary boundary more difficult and sometimes a primer is nessary.
Just for the fun of the mathematics
The water pressure on any point of the hull is equivalent to the weight (force) of the volume (column) of water with the height above it and the area of one square inch.
1 cubic inch of water weights 0.03606 pounds
D: Draft or height of water over thru hull [inches]
A: Thru hull area surface [square inches]
F: Force or weight of the volume water column on thru hull surface [pounds]
F = A x D x 0.03606
P: Pressure [psi = pounds per square inches]
P = F / A = (A x D x 0.03606) / A = D x 0.03606
As seen, the pressure on the submerged hull is only depend on D, the water in inches above it.
1 ft of water over a point on the hull means 12 x 0.03606 = 0.433 psi
Assumed 2 ft of draft over thru hull
24 [inches] x 0.03606 [pounds/cube inches] = 0.866 psi
But the force on a plugged thru hull hole of 2.5 inches of diameter (A = 4.9 square inches) in 2 ft deep would be:
F = 24 [inches] x 0.03606 [pounds/cube inches] x 4.9 [square inches] = 4.2 pounds.
The force is probably what kito meant and with 8 ft: 8 x 12 x 0.433 = 3.5 psi is probably what Ross calculated. Little differences are depending on different assumed inches of water over the thru hull.
Hart
The water pressure on any point of the hull is equivalent to the weight (force) of the volume (column) of water with the height above it and the area of one square inch.
1 cubic inch of water weights 0.03606 pounds
D: Draft or height of water over thru hull [inches]
A: Thru hull area surface [square inches]
F: Force or weight of the volume water column on thru hull surface [pounds]
F = A x D x 0.03606
P: Pressure [psi = pounds per square inches]
P = F / A = (A x D x 0.03606) / A = D x 0.03606
As seen, the pressure on the submerged hull is only depend on D, the water in inches above it.
1 ft of water over a point on the hull means 12 x 0.03606 = 0.433 psi
Assumed 2 ft of draft over thru hull
24 [inches] x 0.03606 [pounds/cube inches] = 0.866 psi
But the force on a plugged thru hull hole of 2.5 inches of diameter (A = 4.9 square inches) in 2 ft deep would be:
F = 24 [inches] x 0.03606 [pounds/cube inches] x 4.9 [square inches] = 4.2 pounds.
The force is probably what kito meant and with 8 ft: 8 x 12 x 0.433 = 3.5 psi is probably what Ross calculated. Little differences are depending on different assumed inches of water over the thru hull.
Hart
Fiberglass isn't that difficult to bevel by hand with something like 36 grit and elbow grease. Just takes a little longer.
You cannot have ever done it! Even with 24 grit and a right angle grinder it takes minutes.
I have done it. So it takes five minutes to bevel ONE hole with a 36 grit flap wheel (with lots of dust spread everywhere instantly) 1/2 hour by hand. The extra time is and sore fingers are worth it to save the awful mess the grinder makes.
But you can be right if you want - I'm ok with that.