Various sites show wood, fiberglass, etc., for backing plates. Has anybody used, say, Corian or HDPV, for backing plate material. Drawbacks?
Thanks.
Thanks.
Backing plates for through hulls
- Thread starter jmkinsfbay
- Start date
JM: Those are all poor bonding plastics that crack under load and creep with few valid structural applications. No.
Ken: He's talking about through hulls, not winches. I assume you misunderstood. Difficult to bond and impossible to grind to match the hull curve.
IMHO fiberglass is the smart way. Just grind to match the hull curve, bond with thickened epoxy (clamp with a center bolt), and you have a strong point that will outlast the boat. No brainer. Yes, you can get a way with wood; I was looking at a rotting through hull backing plate on a friends boat just a few weeks ago.
Ken: He's talking about through hulls, not winches. I assume you misunderstood. Difficult to bond and impossible to grind to match the hull curve.
IMHO fiberglass is the smart way. Just grind to match the hull curve, bond with thickened epoxy (clamp with a center bolt), and you have a strong point that will outlast the boat. No brainer. Yes, you can get a way with wood; I was looking at a rotting through hull backing plate on a friends boat just a few weeks ago.
Ken13559 and thinwater. Thanks for comments. I wouldn't think HDPV (cutting board) would be very hard to shape, and even Corian can be shaped with a file. Regardless, though, is it fairly easy to find pieces of 1/4" or 3/8" fiberglass, so's one doesn't have to go through the laborious and somewhat expensive creation of a plate of fiberglass? Maybe I could find a holed hull that's somebody's yard boat! Take care.
Thru hulls should not see that much structural type loads. Wood works fine if you seal it BEFORE you install. I'm thinking that HDPV would be fine also. Better because it will never rot.
Thanks, again. Think I'll avoid wood for sure - way too many complaints about it softening and decomposing.
The problem with HDPE is you cannot bond it to the hull. Glue won't stick.
You can order small amount of pre-cast FRP from McMaster Carr.
http://www.mcmaster.com/#structural-fiberglass-(frp)/=12ienhu
8537K26 (1/2 x 12") should get you though a few projects. 1/4" is also handy for cleat backings etc.
Backing plates should generally be about 1-1.25 bolt diameters thick, less if bonded to the deck. For through hulls it depends on the starting hull thickness, but 3/4" total, including the plate, should be enough if it is bonded to the hull. If it is not bonded to the hull, it doesn't really strengthen the hull to replace what was drilled out. I've done lots of strength testing for articles.
You can order small amount of pre-cast FRP from McMaster Carr.
http://www.mcmaster.com/#structural-fiberglass-(frp)/=12ienhu
8537K26 (1/2 x 12") should get you though a few projects. 1/4" is also handy for cleat backings etc.
Backing plates should generally be about 1-1.25 bolt diameters thick, less if bonded to the deck. For through hulls it depends on the starting hull thickness, but 3/4" total, including the plate, should be enough if it is bonded to the hull. If it is not bonded to the hull, it doesn't really strengthen the hull to replace what was drilled out. I've done lots of strength testing for articles.
I followed Maine Sail's fine article....
http://www.pbase.com/mainecruising/replacing_thruhulls
.... mostly with a few minor deviations....
http://1fatgmc.com/boat/end-1/endeavour-plumbing/page-4.html
.... and ....
.... used the backing that he recommended,
Sumner
========================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...http://purplesagetradingpost.com/sumner/endeavour-main/endeavour-index.html
Mac Trips to Utah, Idaho, Canada, Florida, Bahamas
http://www.pbase.com/mainecruising/replacing_thruhulls
.... mostly with a few minor deviations....
http://1fatgmc.com/boat/end-1/endeavour-plumbing/page-4.html
.... and ....
.... used the backing that he recommended,
Sumner
========================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...http://purplesagetradingpost.com/sumner/endeavour-main/endeavour-index.html
Mac Trips to Utah, Idaho, Canada, Florida, Bahamas
This is why I always hang on to my scraps of fiberglass... I just take a dozen or so layers and lay them on a plastic sheet, wet out, fold the sheet over and put a car battery on it. Later I cut the cured piece in half and epoxy them together, yields a 1/4" thick fiberglass backing late from a total of 24 layers of 8.5 oz.
At the end of the day it's probably just as well to but pre-fab G-10 or likewise from McMaster-Carr, but this method is somewhat free, used up otherwise useless fiberglass scraps, and in the case of curved hull you could easily do the build up in place to avoid messy grinding later.
At the end of the day it's probably just as well to but pre-fab G-10 or likewise from McMaster-Carr, but this method is somewhat free, used up otherwise useless fiberglass scraps, and in the case of curved hull you could easily do the build up in place to avoid messy grinding later.
Many thanks to everyone for the very helpful comments. I'd read the Maine Sail article (the best, I think) already.
Now, although this should perhaps be a new thread, I'll ask here. My query regarded the engine co-coolant through-hulls. Of all the through-hulls on my boat, those two are the only ones that are visibly corroded. I feel at this point that after replacing them, that I must bond an anode system to the new valve assemblies. My plan is to attach a #8 wire to both through-hulls, then have a dis-connectable #8 wire running out through one of the angled holes in my cockpit Plexiglas, so's I can drop a zinc or aluminum anode over the side while in berth. I'd rather not drill a new hole in the transom for same, but am looking for ideas from other boaters who might have done something similar. BTW, there's no bonding plate or similar running through the boat or in the engine compartment.
Now, although this should perhaps be a new thread, I'll ask here. My query regarded the engine co-coolant through-hulls. Of all the through-hulls on my boat, those two are the only ones that are visibly corroded. I feel at this point that after replacing them, that I must bond an anode system to the new valve assemblies. My plan is to attach a #8 wire to both through-hulls, then have a dis-connectable #8 wire running out through one of the angled holes in my cockpit Plexiglas, so's I can drop a zinc or aluminum anode over the side while in berth. I'd rather not drill a new hole in the transom for same, but am looking for ideas from other boaters who might have done something similar. BTW, there's no bonding plate or similar running through the boat or in the engine compartment.
Some sources such as West Marine are advising not grounding thru-hulls to some extent...
"Do not bond any thru-hulls or other immersed metal that can be electrically isolated. Specifically, keep your metal keel/ballast, your metal rudder shaft, your engine/prop, and all thru-hulls electrically isolated, from each other, and from the engine."
http://www.westmarine.com/WestAdvisor/Marine-Grounding-Systems
My thru-hulls were tied together when we bought the Endeavour and I have not tied them back together and don't intend to. Maybe do some more reading on the subject and decide what you feel comfortable with,
Sumner
================================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...
Mac Trips to Utah, Idaho, Canada, Florida, Bahamas
"Do not bond any thru-hulls or other immersed metal that can be electrically isolated. Specifically, keep your metal keel/ballast, your metal rudder shaft, your engine/prop, and all thru-hulls electrically isolated, from each other, and from the engine."
http://www.westmarine.com/WestAdvisor/Marine-Grounding-Systems
My thru-hulls were tied together when we bought the Endeavour and I have not tied them back together and don't intend to. Maybe do some more reading on the subject and decide what you feel comfortable with,
Sumner
================================================================
1300 miles to The Bahamas and Back in the Mac...
Endeavour 37 Mods...
MacGregor 26-S Mods...
Mac Trips to Utah, Idaho, Canada, Florida, Bahamas
I agree with Sumner. Really, all you are doing is adding the thruhulls into an equation when they are not already connected otherwise inside the boats that is an electrical path. I think you are making them worse by making them a path for electric flow. JM, when you say "corroded", do you mean that scuzzy stuff like green frog skin?
Good thoughts, and I'd read about +/- bonding through-hulls, etc. The corrosion there is not only the "scuzzy green stuff like frog skin", but there is some crystalline corrosion also. One thru-hull (3/4") is for the coolant exchange, and is pumped; the other (1/2") is just passive cooling for the shaft. Boatworks guys looked at them today and thought that they were not in immediate danger, "just clean them up". Now, there is no source of electrical connection between those thru-hulls, and no source of connection to anything else down there, that is, they are completely isolated from each other and from any other metal parts. No moisture, etc. So I'm nervous about not tying them to an anode; are any of you guys saying that I should just leave them alone? And at what point would you say "enough is enough", and haul the boat out and replace them?
Thanks again.
Thanks again.
If you are seeing green residue and crystals you more likely have a seeping thru-hull. Those are salt crystals, and copper oxide leaching out of the fitting. Your thru-hulls should not be bonded to the vessel grounding system, just make certain the outer portion exposed to seawater are not painted with copper bottom paint. Prime them with epoxy barrier paint
MaineSail has several articles here on replacing through hulls, and backing plates, etc: http://www.pbase.com/mainecruising/boat_projects