Originally Posted by danielgoldberg
Curious, what are the reasons?
The reason I'd like to do it the way I'm planning is that the through hulls are installed with 5200, so getting them out will not be without heartache. Plus, if I pull the through hulls I'm sure I'll be doing something that will have an impact on the warranty, or at least the builder certainly will claim that in the future if there is a problem, whereas merely adding flanged adaptors cannot possibly give rise to such an argument. (And Dawg, because I'm doing this over the winter, I will have sailed the boat a bit by then, and believe me I'll be checking the through hulls, so if they were not bedded properly in the first place presumably I'll learn that this season. In any event, as noted, if they're not bedded properly now, I have recourse; if I pull them and then have a problem . . . ) Plus, I actually don't plan to through bolt the flange to the hull. I know, I know, but I just don't like the idea of increasing the number of below-the-waterline holes in the hull by a factor of three. I'm planning to 5200 the backing plate to the hull, then 5200 the flange to the backing plate, and screw the flange to the backing plate (with screws deep enough to get bite, but not deep enough to go through the backing plate to the hull). Assuming I can cut the through hulls to size with them already installed, this should not present a problem, unless I'm missing something.
- The fit between the through hull and backing plate should be a tight fit with the entire hole not much bigger than the OD of the thru-hulls threads. This is critical for the upper flange sealing properly to the backing plate. The hole for the thru-hull retaining nut will be BIGGER than the bevel for the marine sealant in the base of the flange! A bead of marine sealant 3/4 of an inch deep by a 3/8 thick diameter will NOT seal well after you have spun it around threading it onto the thru-hull.
- The thru-hull is designed to be threaded into a seacock or flange that has already been mounted to the hull. The thru-hull is tightened with a step wrench and a large pipe wrench quite tightly.
You are trying to;
Cut the thru-hull to length while installed which could damage the integrity of the seal. It will also be FAR more difficult to do this in the boat than you assume and also get a clean cut with threads that will work.
Thread the flange onto an existing thru-hull which needs to be done with lots of torque. The surface area of the flange is MUCH greater than the little rim that makes contact on a thru-hulls mushroom head. This increased surface area will most likely not allow the proper torque. Spinning a thru-hull head against fiberglass has much less resistance than spinning a 5-6" wide flange. Applying the proper torque could either spin the thru-hull, thus damaging the original seal, or not allow enough torque for a proper fit & seal.
- The backing plate should be full, meaning no voids to account for the nut you would be sliding it over, as the entire premise is to strengthen the hull and prevent movement.
- In the future, if the thru-hull leaks because you never re-did or corrected the 9th grade drop outs mistakes, made at the factory, how on earth will you get to the thru-hull retaining nut buried in the marine sealant to remove and re-bed the thru-hulls?
Considering I owned a brand new boat and went through a full re-bedding, after ONE season, I do NOT trust any factory bedding job, to a high school drop out, especially one bellow the waterline. The guys doing the grunge jobs at the factory, like bedding, are NOT the highest skilled guys in the plant trust me!!
Having worked in boat yards in my younger days, and having R&R'd perhaps 100+ seacocks, I can assure you that seacocks bedded with 5200 will come out, any number of ways, including a 4" angle grinder. I've always had luck with a heat gun and a pipe wrench. You ruin the threads but the thru-hull is a minimal expense in this project..
If this is the method you plan on using I'd consider just leaving them the way they are. I don't understand how you'd void any warranty by adding or changing a thru-hull. In fact the builder may claim adding the flange is what caused the integrity damage or leak of the thru-hull, if you have one, as I pointed out in the pit falls above.
Thru-hulls are meant to be threaded in last to an already secure, & top side bedded, seacock or flange.