Standard Horizon Speed Transducer

[bhstech]

I have a ,new to me, C-27 with an older S-H model MD100 Multi data Instrument. It is the earlier version of the MD150. The only thing it has been doing is giving me depth. Before I put it in the water, the underside seemed to have two transducers. I assumed one had gone bad and a new one installed. Why not just replace the old one? I had no idea.
The other day I was contemplating the macerator when I saw what appears to be a speed transducer just lying there in the same locker as the topside of the depth transducer and the macerator etc.
Since the boat is in the water, trying to install the transducer now could cause a few problems.
Does anyone have a cross sectional view of the transducer or the mounting thru hull? The transducer has a paddle wheel and about 3 o-rings. The I assume the one thru hull without any wires coming out of it has a plug that looks like the other one that is the depth sounder. Is this possible? I've looked at the S-H website and the manual, both have precious little information.

[GordMay]

Yes, the "unwired" insert is very likely a blank plug.
You should be able to effect the change out (plug to x'ducer) quickly enough that you only take in about a cup (or so) of water.

[svHyLyte]

Originally Posted by bhstech

I have a ,new to me, C-27 with an older S-H model MD100 Multi data Instrument. It is the earlier version of the MD150. The only thing it has been doing is giving me depth. Before I put it in the water, the underside seemed to have two transducers. I assumed one had gone bad and a new one installed. Why not just replace the old one? I had no idea.
The other day I was contemplating the macerator when I saw what appears to be a speed transducer just lying there in the same locker as the topside of the depth transducer and the macerator etc.
Since the boat is in the water, trying to install the transducer now could cause a few problems.
Does anyone have a cross sectional view of the transducer or the mounting thru hull? The transducer has a paddle wheel and about 3 o-rings. The I assume the one thru hull without any wires coming out of it has a plug that looks like the other one that is the depth sounder. Is this possible? I've looked at the S-H website and the manual, both have precious little information.

Ensure that the paddle-wheel assembly is clean and the paddles free spinning. Note that the interior end of the assembly has an arrow embossed on it next to the cable to indicate the correct orientation for installation. Take an old towel or, better, a chamois cloth and lay it, loosely, around the through-hill fitting to collect the water that will spill in when you pull the dumb plug. Pull the locking pin in the plug, loosen the locking ring and work the dumb plug free by rotating it a bit. Then pull the plug with one hand and insert the transducer with the other (that can be done within a second or so and you'll only get a cup-full or so of water in the boat-caught by your towel), ensure the orientation is correct, tighten the locking collar and insert the security pin through the transducer. To ensure the transducer is easy to remove, it helps to wipe a little non-petroleum grease on the sides of the plug. FWIW, I also apply a little film of Neosporin antiseptic cream to the paddle-wheel which slows the development of growth that inhibits the free spinning of the wheel somewhat. The dumb-plug should be retained in the vicinity of the through-hull with a lanyard.

FWIW...

[Jim Cate]

FWIW, I have the same model SH. On ours, the through-hull fitting has a built in check valve flap that limits ingress of water whilst you make the swap. Doesn't completely stop it, but we typically get only a few cc's of water each time we pull the transducer.

The first time you do it will be slightly intimidating (or at least it was for me) but now we routinely pull the paddlewheel out if the boat will not be moved for a while... cuts way down on fouling.

Cheers,

Jim

[bhstech]

OK maybe I'll get the courage to try this. I was talking to someone today and he said it is very common practice, or use to be, for racers to pull the speed transducers out all the time because leaving them in would cause them to gum up with growth etc. and make them loose accuracy. However, with modern GPS you get a COG speed than is much nor usable than how much water is flowing by a spinning wheel. I'm on a Lake so I'm not getting flow of currents, tides etc.
What kind, specifically, of lubricants do you recommend? Would mineral oil be OK if petroleum is NG?

[Jim Cate]

Originally Posted by bhstech

OK maybe I'll get the courage to try this. I was talking to someone today and he said it is very common practice, or use to be, for racers to pull the speed transducers out all the time because leaving them in would cause them to gum up with growth etc. and make them loose accuracy. However, with modern GPS you get a COG speed than is much nor usable than how much water is flowing by a spinning wheel. I'm on a Lake so I'm not getting flow of currents, tides etc.
What kind, specifically, of lubricants do you recommend? Would mineral oil be OK if petroleum is NG?

We have used both silicone grease and plain old Vaseline. The silicone lasts longer, but both work just fine. Have a look at the o-rings if the transducer has been out for a long while. Cheap and easy to replace, and you don't want a leak to develop due to a perished o-ring.

And by the way, if you are using the speed data for trimming sails, the speed through the water is more useful than SOG (although on a lake this isn't so true, I guess).

Cheers,

Jim