Presented by popular demand, the details of replacing the raw water intake through hull on Alchemie, our H34. Next up is a spine transplant after spending hours hunched over in the aft compartment changing it, the PSS bellows and replacing the old shaft coupling with a new split coupling.

Typically we find a blockage in our raw water line after 1 1/2 years following a haul out. We can go as much as 3 1/2 years between haul outs before the diver starts complaining. So, each time we go out we usually have to pull the intake hose off the strainer (relocated to the front of the engine compartment) and give it a blast from the air horn. I thought that enlarging the through hull from 1/2 inch to 3/4 inch might give us some margin in the frequency of having to clear any obstructions. Time will tell. From the pictures we started with (1) the 1/2 ball valve (changed from a gate valve many years ago). This ball valve also possessed the classic NPT-NPS thread mis-match, so it needed to go anyway. After removing the bronze ball valve, naturally, it was impossible to unscrew the nut more than a couple of turns because it was discovered later that blue Locktite was used. Out came the Sawzall and (1a) the mushroom head was removed. I was so fast that my wife couldnt get the camera ready in time, so the picture shows me holding it place after it was cut off and not sawing with my fingers anywhere near the saw. Inside, the hole in the pan liner was a bit too small to work in and set the new plywood backer, so I drilled it out farther with a 4 hole saw (2), then used a small disk sander to clean up the hull surface (3). Back on the outside, I determined the original hole was 7/8 in diameter, so I pushed that size hole saw into the hull (4). That fit inside a 1 1/8 hole saw (5) that was the correct size for the 3/4 replacement through hull and acted as a guide resulting in a properly bored enlargement (6). Later I slightly chamfered the gel coat arount the hole to break the sharp edge. At this point I was going to go with a Bronze replacement like the old one, so I test fit everything just to be sure there would be enough threads exposed with the hull thickness and the 3/8 epoxy saturated plywood backer. After reading a few more posts and answering one where this is not the best practice (even though Forespar says it can be done), I took my own advice and bought a Marelon through hull to maintain consistant materials. The picture comparing the 3 through hulls (7a) shows the differences in the original 1/2 versus the two 3/4 bores. Note the magic marker arrow on the bronze fitting. During the dry fit process, I tightened everything up and then alternately loosened, rotated the assembly and re-tightened the nut until the valve handle pointed fore and aft where I could reach it with the engine cover open and operate the valve. The old one had the handle behind the valve and required unloading the back berth to gain access to the valve. Not very convienent or quick. Once the orientation was established, a matching mark was made on the hull to retain orientation. Everything was disassembled and the through hull and backer were coated with 3M 4200. Enough sealant was applied to squish out from the mushroom head and fill the gap between the hull and threads up to the top of the plywood. Some probably got under the nut as well, but was not deliberately coated. The valve was installed using Teflon tape as the sealant. I managed to get 6 1/2 turns on it before bottoming out on the nut. Later I installed a new 3/4 tailpiece and 3/4 rubber hose up to the strainer. The old hose was 5/8. I could not get the old 1/2 NPT to 5/8 barbed hose adapter off the strainer. The 3/4 hose was a loose fit, but the hose clamps cinched it up tight. I actually might like that fit as whenever I had to clear the line with my air horn, it was really hard to get the rubber hose off that fitting. Ill keep an eye on it for air leaks. The final picture (9) shows the valve and the rest of the project including a new bellows on my PSS dripless seal and a new split coupling for the shaft. It took a half day to get that old coupling off using the technique described by Main Sail and others of sandwiching a spacer between the transmission and prop shafts and squeezing it off with longer bolts. Never again! Motoring back from Berkeley to Alameda (1 1/2 hours) resulted in no leaks and I think about 5 degrees cooler engine temperature. I did not take note of the water flow rate (Ralph Johnstone likes my Rotometer on the strainer). Ill check that later.

All in all a worthwhile upgrade eliminating the thread mismatch, increasing flow margin and orienting the valve more convienently.