Thru hull questions

gplume · Post by **gplume** » May 8th, '08, 11:06

Got past what to buy from preciuous inputs, and have two new bronze groco seacocks to install this weeked.

??? to those in the know;

2.) I have several pieces of "seaboard" HDPE (Highdensitypolyethelene) about 5/8 on an inch thick that I used for another project. These look like good candidates for backing pads vs marine plywood. They claim to be impervious to water. Any opinions?? or just stick with good old marine plywood. I ask because the original pads were quite soft when I removed them, so I am thinking wood is not the most robust option,

2.) For the 3 bolts around the periphery of the seacock, bolt thru the hill, or just bolt into the backing pad. My inclination is to bolt thru the hull. Looking for opinions from more experienced folks.

Note - one of the old sea cocks had this arangement and one did not.

Any feedback is appreciated.

Giff

CaptPatrick · Post by **CaptPatrick** » May 8th, '08, 13:37

Gif,

As always, I don't like PE/Starboard... It can and has been used, but you won't find anything that will bond it to the hull and, because of the flexibility of the material, if the through hull unit is subjected to lateral force, (something trying to bend/break it over), the only support at the base is somewhat more than the diameter of the fitting.

In my estimation, 3/4" epoxy coated plywood is far stronger and will last for plenty of years. When & if it does get wet, dig it out & replace it again. Done properly, water isn't going to get to the wood in less than 5 years...

You need to fully through bolt the fitting to the hull. This gives you both a mechanical attachment of the backing pad along with the 5200 bonding.

Br,

Patrick

Kevin · Post by **Kevin** » May 8th, '08, 18:49

I am curious. Why do boat manufactures put those extra wood pieces in at the thru hull? Had a couple out when I repowered and thought that the glass was so thick why bother with them. It seems as most thru hulls on the average joe boater has rotten wood which ends up falling out and then there is a 1/2 inch gap between the nut and the hull, leaving it suspect to leaking. I know we here are not the average boater though.

jspiezio · Post by **jspiezio** » May 8th, '08, 19:48

Someone I know told me they use 5/8 arena grade plexiglass (or something similar) as a backing plate. Have you guys ever heard of this? Thoughts?

bob lico · Post by **bob lico** » May 8th, '08, 20:32

is it possible for you to purchase "epie" .this is a wood from the amazon rain forest.use all over eastern long island for decking.you only need a small piece.try a real lumber yard in R.I not a home center!!epie will outlast the bertram it totally impervios to water.i used it for all thru hulls and sister the stringers for motor mounts with it.a bitch to drill but you know how to due the right thing.this is the only material to use for thru hull backing trust me.

randall · Post by **randall** » May 8th, '08, 22:04

its interesting stuff (epie)... i built a large pool deck out of it when i was a carpenter. first day i threw a chunk in the pool and it didnt even try to float. we sealed every cut end with a wax coating...it loves to split....so i would pay attention to that. i have a block about 14x 14 x 4....you wouldnt believe how heavy it is. the stuff would make good ballast.

jspiezio · Post by **jspiezio** » May 8th, '08, 22:54

.it loves to split....so i would pay attention to that.

Good advice there. If you are using wood, nothing can be stronger than ply.

Buju · Post by **Buju** » May 9th, '08, 05:22

Ipe "AKA" Brazilian Walnut... I wouldn't say its impervious to water at all... More so than most woods, but not nearly as much so as Teak. I've had to refinish a couple of Ipe decks, and have come across some rot and a lot of splitting. [/b]

bob lico · Post by **bob lico** » May 9th, '08, 10:01

randall i mention how hard it was to drill. i assume anybody using it for a thru hull would drill it.i never had a piece split.i seen decks 2000sg. feet without a split but plenty of drillbits!by nature the tree grows in a waterlog or sometimes surmerged state how could it rot on a deck situation unless there are other issues.

randall · Post by **randall** » May 9th, '08, 12:12

bob....its hard but its wood....all wood will rot(eventually) in a submerged unprotected dead state.(very very slowly in full logs in very cold water) lots of trees grow in swamps...mangrove and cyprus for example ...but they rot away quite fast when they die.......the wood on the deck is dead...or should be. for fun i started trying to drive a 10 penny nail through 5/4 ipe with a framing hammer. to sketchy to try on anything you wanted to keep but just for grins on scrap i got so i could do it half the time......kind of a karate' deal.

if the deck is in the sun and gets wet and the cut ends arent sealed it is very prone to splitting...look at the lumber yard stock...all the ends are sealed...

bob lico · Post by **bob lico** » May 9th, '08, 13:48

well randall i have to say you have a point there(all wood rots when it`s dead) as far as using it for thru hull . i take my time and put two coats of unthicken epoxy and awlgrip primer after i drill the thru hull diameter with a hole saw.this way i can epoxy the raw edge from the hole saw.then i cover the entire bottom of the block with 5200 and smear the inside diameter of the hole with the 5200,insert the thru hull and tighten down the flange nut untill the 5200 ozes out.---never leak and will not rot at least not in my life time.

CaptPatrick · Post by **CaptPatrick** » May 9th, '08, 14:34

bob lico wrote:well randall i have to say you have a point there(all wood rots when it`s dead) as far as using it for thru hull . i take my time and put two coats of unthicken epoxy and awlgrip primer after i drill the thru hull diameter with a hole saw.this way i can epoxy the raw edge from the hole saw.then i cover the entire bottom of the block with 5200 and smear the inside diameter of the hole with the 5200,insert the thru hull and tighten down the flange nut untill the 5200 ozes out.---never leak and will not rot at least not in my life time.

Same works for plywood & it can't split due to the 0Âº/90Âº orientation of the ply...

Now if you want, (imho), the ulitmate material for the job see: PVC Foam Board as an Alternative to Plywood. Rigid PVC can also be used & both will accept 5200 bonding well.

I am curious. Why do boat manufactures put those extra wood pieces in at the thru hull? Had a couple out when I repowered and thought that the glass was so thick why bother with them. It seems as most thru hulls on the average joe boater has rotten wood which ends up falling out and then there is a 1/2 inch gap between the nut and the hull, leaving it suspect to leaking. I know we here are not the average boater though.

The reason for adding a thick backing between the hull & flange of the fitting is to increase the overall thickness, making a much stronger support to the fitting's tube.

Br,

Patrick

jspiezio · Post by **jspiezio** » May 9th, '08, 15:52

Capt Pat seems like you answered this question and one that I had asked on another thread in one fell swoop.....

bertram31.com

Thru hull questions

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