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Date Posted: - Thursday - 02/ 5/09 - 1:37pm
Author: Lyle Harris
Subject: Thru Hull Replacement Question, M31

So I'm having Starlight hauled out next week for bottom cleaning, inspection, gelcoat repair, and bottom paint. This boat has very old bronze gate valves for the head and drains, which I will replace.
I'm planning to replace the thru-hulls as well, but I've never seen them, and don't know how many there are below the water line. I'm counting three, but wonder if I've missed one.
Would anyone know which is typical for the M31; flush or mushroom-flange Thru hulls? I can see the on at the Head is a 1.5 in. unit, but haven't been able to get to the others, yet. Obviously, all will be known when the boat is hauled out next week, but I'd really like to have the replacements on hand and start working than spending time at the store.

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[> Through-hulls -- Steve M-32 #59, - Thursday - 02/ 5/09 - 3:03pm

I have six. Three in the head for the sink drain, the head intake and the head overboard discharge. Two for the cockpit drains one of which is also tied in as the galley sink drain. One more the raw water intakewhich is also used as an intake for a raw water washdown pump. All of them are flush mounted except for the raw water intake which has a mushroom head. Given the age of the boats I have no idea what's original or not but mine hasn't modified too much so I think this is close. There are also two above the water line for the manual bilge pump and the engine exhaust.

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[> [> Thru-hulls -- Gitano (M31#95), - Thursday - 02/ 5/09 - 3:36pm

I have 8 total. Four in the head (three same as Lyle's, and an additional 1/2" for seawater intake to the water maker), and two at the engine intake (one for the engine heat exchanger raw water, one for the galley sink grunge faucet), and two cockpit drains. I think originally, on a stock M31, there would have only been 6, as with Lyle's boat.

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[> [> [> Sory Steve and Lyle -- Gitano, - Thursday - 02/ 5/09 - 3:37pm

I got your two names mixed up.

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[> [> [> [> Thru Hull Replacement Question, M31 -- Lyle Harris, - Thursday - 02/ 5/09 - 3:56pm

Thanks for the information. I'm probably better off waiting until the boat is up and out before buying anything. I don't believe my boat has had a refit of any kind in a decade, and would be surprised if any more than three thru-hulls were below the water line.

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[> [> [> [> [> Through-hulls -- Steve M-32 #59, - Thursday - 02/ 5/09 - 7:08pm

If you have a 1.5" in the head you should also have a .75" for the water intake on the toilet. That one should be forward of the larger outlet. Look under the sink and there should be one there for the drain. Pull off the cabinet containing the sink and your raw water intake should be right there in front next to the icebox. There are two large (1.5"?) for the cockpit drains as they drain under the waterline. They are visible left and right of the transmission about 18" away. If you don't have at least those then someone has blanked some off and I would look very carefully for those areas to check on the quality of the patch job.

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[> [> [> [> [> [> Cockpit Drain(s) -- Gitano, - Friday - 02/ 6/09 - 12:43pm

I hope that you have at least one cockpit drain to drain rainwater or splashing waves taken on when under sail. Gitana Vela (M31#95) has two cockpit drains located just as described above. The galley sink drain ties into the starboard cockpit drain thru-hull line. The port side thru-hull drains only the cockpit floor drain.

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[> [> [> Thru hulls -- Kathy Campbell SHADOW M32-#3, - Thursday - 02/ 5/09 - 10:06pm

Hi Northern Neighbors, Guess what! It appears that some of your rain has escaped an is down here getting Shadow an me a bit wet. Don't laugh we've had a drought in Southern California, so thanks. Shadow has three thru hulls in the head area and three thru hulls aft, engine raw water intake and port and starboard cockpit drains. As far as the two head thru hull on Shadow I've capped them off. Down here any ports of call are off limits to flushing into the open water, so for the time being I have a !! porta potty!! Hopefully in the future maybe one of thoughts Air Head, composting toilets? Just a little note on the marine plywood, joubert okoume BS1088. alliedveneer.com carries 48"x98" but they did have 5x10 pieces. If enough interest was shown they may order more. For doing the back cockpit you would only need two pieces of plywood, but maybe it would be different with the 31. Anyway it was just a thought. 48x98 $114.00. Yours truly Kathy

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[> Thru hulls -- Dan M32 #36 Independence, - Friday - 02/ 6/09 - 11:10pm

What about depth sounder transducers and knot meter sending units? More holes in the hull? My M32 came with a big chunk of wood that the depth sounder sending unit is mounted in. It sticks out from the hull alot and isn't very fair. I assume that this was not original. Were depth sounders and knot meters original equipment? How are the sending units mounted on your boats?

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[> [> Thru hulls -- Kathy Campbell SHADOW M32-#3, - Saturday - 02/ 7/09 - 1:54pm

Dan, I remember your boat then it was for sale. I didn't know the trailer that went with it was such a nice one. Like George Muller, don't sell the trailer without the boat. I would have bought it if I didn't already have a boat. Anyway, Shadow has a BIG chunk of wood on the port side which had an old Ocean navigator depth sounder. After 24 years of dragging this chunk of wood under the hull- it's out of here. A lead line will always work, but they have some pretty nice, flush thru hulls. One that looks like it would work is the Airmar's KW B164 (tilted thru-hull. Price is a problem with it. www.airmar.com.

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[> [> thru hulls -- Dan M32 #36 Independence, - Saturday - 02/ 7/09 - 2:47pm

Sounds like we have the same setup, maybe that was how they were sold. Seems a bit mickey mouse. I,m thinking about fairing in a small more or less level flat place to mount the two sending units in.
It was a nice trailer. George let me use it to haul the boat from Salt Lake to San Juan Island and in exchange I then found a buyer for the trailer. A guy From Atlanta,Ga. flew out to Seattle, bought an old 1 ton truck and pulled it back.

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[> [> [> Airmar in hull transducer -- Jared Kibele, - Monday - 02/ 9/09 - 5:11pm

I just installed an Airmar in-hull transducer. It was under $100, glued to the hull with a silcone sealant, and works great with my Garmin sounder and chartplotter. Here's the airmar link: http://www.airmartechnology.com/airmar2005/ex20/RMProducts/ElectCat.asp?ProdID=52&Man=All&PageNo=99

That being said, you may be able to use your old transducer with a new sounder. ...it depends on how old the transducer is. Most of them are dual frequency these days.

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[> [> [> [> Wow. That's cool -- Randall, - Monday - 02/ 9/09 - 7:40pm

I don't see anywhere a spec for the thickness of hull it can pass through and worry when it says "good for racing sailboats up to 25'". Thin hulled little bastards! But you're using it, so all must be good, no? Where did you position it?

My issue is more w/the readouts. Either they have gotten smaller or my eyes are less strong, but at night I can barely make out what they're telling me. So it's time for an upgrade...at least in font size!

Anyone use the "new wireless" units?

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[> [> [> [> [> Thick hull -- Jared Kibele, - Thursday - 02/19/09 - 11:41am

Hi Randall. I mounted my transducer under the aft-most drawer in the port settee. It turned out that was the only place I could find a 22 degree or less deadrise angle (this model of transducer can mount on a surface with 0 - 22 degrees). From my understanding, hull thickness shouldn't really matter. Sonar signals have problems crossing boundaries between different types of material but shouldn't attenuate much based on the thickness of the fiberglass. So a thick solid fiberglass hull works fine but a thin cored hull wouldn't work.

My transducer is hooked into a garmin sounder box (gsd 22: https://buy.garmin.com/shop/shop.do?pID=288) and the sounder is hooked to a garmin 4208 chartplotter (https://buy.garmin.com/shop/shop.do?pID=8113). The 4208 also works as my radar display. You can display the depth soundings in a whole slew of different ways. The whole mess is also hooked up with my autopilot.

...I went a little nuts with the electronics. I like that stuff.

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[> [> [> Depth sounders -- Dan M32 #36 Independence, - Tuesday - 02/10/09 - 1:20am

I'm with you Randal in reguards to the small display size.I recently put a Humminbird sounder in my San Juan 24 and it's about 2" in dia. and it's hard to read sometimes. It replaced a 5" dia. Standard Horizon that stopped working after only 6 yrs. I wanted to replace it with one the same size but apparently all the instrument makers got together and decided it would be funny if they stopped making 5" dia. to see what people would do with all tose 5" holes in their boats. I had to make a plastic filler for the hole. I think the 2" instruments are intended to go in a dashboard like on a powerboat. Anyway the transducer is a glued in hull type. I've only used the boat a few times since installing it and I've gotten some wacky readings. The old one was a Standard Horizon with a in hull transducer that was in mineral oil and it worked great until it stopped. I was considering going to a fishfinder but they're all rectangular and not made to go in a bulkhead. Looking on line for depth sounders recently( I'm starting to research all the things I'll need for my Mariner ) I noticed there is a lot of transducers for sale w/o the instrument so I guess some must be interchangable as long as they work on the same frequency. I also noticed that some are made with the transducer at an angle in the thu hull which is good but they are expensive. One more thing while I'm venting, why do alot of the new sounders read in tenths of a foot? Why could it possibly matter that it's 276.3 ft. deep?

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[> [> [> [> Ha! Tenths of feet -- Randall, - Tuesday - 02/10/09 - 1:51am

Thanks Dan. It's funny to be learning about many things--including eye site--from Murre. Only a couple years ago and while working in tight quarters, I noticed that I couldn't quite see the fastener nor the hole I was attempting to guide it into. I thought at first I'd inhaled too many epoxy fumes. But then Joanna reminded me I'm over 40. One can always depend on Joanna for the important stuff--like putting me in my place.

Wacky readings? I get those from my through hull unit...due to really muddy water...transponder out of the water, etc. But what do you mean by whacky?

Tenths of feet. That's funny. Now, let's see, I draw 3.8 feet and the depth is 276.3, so how many tenths of minutes till I run aground?

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[> [> [> [> [> thru hulls -- Dan M32 #36 Independence, - Tuesday - 02/10/09 - 12:40pm

By wacky readings I meant that as I was sailing the soundings seemed ok and then they would fluctuate wildly. I knew It wasn't reading the bottom accurately. I never had that problem with any of the other sounders on any of my past boats. I know that in certain circumstances sounders will jump around. When I was sailing from Panama to Equador last June on a Passport 40 the sounder would occasionaly show 50 or 80 feet but we were 300 miles off shore. The captain said it was temp. changes. I just not ready to trust the new sounder yet. I think a hole though the hull is probably the best for a transducer.

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[> [> Murre's bum with transducer -- Randall, Murre, M31, - Monday - 02/ 9/09 - 1:42am

Murre's depth sounding and knot meter units are a little different. A couple photos from below are attached. They are both on the port side, both accessable from the port settee. Both are pretty flush. I've not done anything with them, so don't know anything beyond that.

But that does lead to a question of my own. I want to change out the knot and depth meter read-outs in the cockpit. Will I need to change the underwater units as well? Or can I simply plug in new read-outs into existing stuff?

click to enlarge.

From the side:
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from below:
Free Image Hosting at www.ImageShack.us

QuickPost Quickpost this image to Myspace, Digg, Facebook, and others!title="QuickPost">QuickPost Quickpost this image to Myspace, Digg, Facebook, and others!

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[> [> [> transducers and thru-hulls -- Lyle Harris, - Monday - 02/ 9/09 - 4:42pm

HI Randall,
Don't know if it's helpful, but there are transducers that you just epoxy to the inside of the hull below the waterline, and don't make any penetrations. That may be one way to go.
I ended up using something like this on my current in-the-water sailboat because the depth finder was shot and I couldn't find anything compatible with the existing transducer.

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[> [> [> [> depth meter transducer -- Ardian, - Monday - 03/23/09 - 10:16pm

I installed the transducer inside the hull and it does work great since 2-3 years .I bought a hummingbird matrix 12 . To start i did build the dam that will hold the resin . so , i did cut in a form of triangle a piece of cartoon and used epoxy resin in to almost vertical sides to glue it to the hull . Of course after i cleaned the hull from the paint and dirt . Once cured i mixed the resin with a very slow hardener so the air bubbles created from mixing it will be gone by the time it cure .Because the air bubbles will create problem if there. sink the transducer but be careful that it must not move till it cures and also i place it facing fore a few degress . And the next day was done. Just be careful because not all the transducers work from inside the hull. Hope that this will help . Good luck. Ardian.

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[> [> transducers an sounders -- Kathy Campbell SHADOW M32-#3, - Monday - 02/ 9/09 - 10:49pm

OK, Here it is from the lead line specialist. There was an article in December SAIL magazine ' SOUNDER ROUNDUP '08. They tested sounders an transducers. It was brought out that impedance has to be matched between the transducer and the sounder to get the best readings. M-A-R-K twain, Kathy

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[> [> [> Final note on Thru-Hulls -- Lyle Harris, - Tuesday - 03/10/09 - 1:14pm

Follow-up to how many thru-hulls below the waterline on an M31... I'd originally thought there would be three thru-hulls below the waterline to replace. Turns out there were six. I'm fairly certain this was the original configuration for the M31. There are three in the Head, and three in cockpit area.
The cockpit drains and head (toilet)drain are all 1.5 inch size. The toilet saltwater intake and head sink intake are 3/4 inch, and the engine raw-water intake is 1 inch. All thru-hulls were mushroom-flanged bronze.
I suppose it could be different for other boats, but this is what I found.

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