Transducer... in a seacock?

[justanothersailboat]

Speed transducers don't seem to be much good when they get fouled. Most (all?) seem to have some arrangement where you can take them out and stop up the hole while you clean them. Many people become just fine doing that, but it is daunting for others, and it rather restricts the transducer to somewhere you don't mind getting wet.

Is there any particular reason why someone can't fit a large seacock to a through-hull, then feed the transducer through it? then it could be withdrawn and the seacock closed while the transducer is still in the pipe, avoiding letting in any water. The transducer would need to be on some kind of fitting to make sure it settled at the right height and was an exact fit, but this is probably simple lathe work. Anything that made it easier to remove would also reduce the need to clean it, since it'd encourage taking it out after each use. (And when I'm not on the boat I'd cap the pipe, so then there's a closed seacock connected to a short straight closed pipe, which is no more concerning than any other seacock)

I've never seen this done, or heard of it. That makes me think there must be a good reason not to do this. What am I missing?

 

[RunAgroundHard]

Basically the transducer housing is designed to fit the transducer and seal it. Introducing a big valve around that would require to be sized to allow a hand in to undo the cap and pull the transducer, as well as somehow sealing around the arm. Incredibly more hassle than just pulling the transducer and fitting the blanking cap.

Many transducers have a flap that closes when the transducer is withdrawn that somewhat isolates the water flow. All should have a blanking cap to isolate the opening.

To be honest, it’s not an issue that demands a solution, even for those with no isolating flaps.

There are lots of devices in industry for withdrawing instruments from pressurised pipes and vessels, that are pressurised. There are also tubes devices that bring instruments up above sea level.

I think the market in the leisure industry, even DIY, for a retrofit device, would be almost non existent as solutions already exist.

 

[Sandy]

I have seen one boat with a length of brown plumbing pipe glassed onto the hull with the trough hull at the bottom of the pipe and know know why this is not common practice.

With practice you can remove the transducer and fit the blanking plate in less than 10 seconds and have less than a litre of seawater in the boat. You will not sink the boat, you will not die.

 

[Stemar]

I have seen one boat with a length of brown plumbing pipe glassed onto the hull with the trough hull at the bottom of the pipe and know know why this is not common practice.

With practice you can remove the transducer and fit the blanking plate in less than 10 seconds and have less than a litre of seawater in the boat. You will not sink the boat, you will not die.

I can imagine the faff of withdrawing it, then getting it back in exactly the right place to work without pushing it all the way through.

As for a seacock, how are you going to close it with the cable in the way? You'd have to pull it all the way up beyond the cock, so same faff.

 

[justanothersailboat]

I don't think I'll sink it. I just really hate letting water get in certain less-accessible parts of the bilge and it occurred to me that an actual valve would do a neat job. A litre in a certain spot is a right nuisance for me.

Sandy, that pipe arrangement sounds like it would functionally work, was it just too cumbersome? I don't think I would have room...

Stemar, I'm imagining that the cock is open when the sensor is in place, with the sensor filling the tube (probably in a machined rod that is an exact fit). Then taking the sensor out to just above the seacock, closing it, and removing it the rest of the way. Not trying to close it on the cable.

 

[ylop]

I think the answer is probably “there is no reason why not” but you’ll need to go to a lot of effort to make sure the transducer is sitting in clean flow of water, can be easily inserted and removed etc, and will need a taller vertical tube inside the hull (if I understood your proposal correctly). What you pull out will still be wet, slimy and potentially crawling in little critters so I’m not sure it really opens up better locations.

However it does raise a question which perhaps helps the same problem… what do people use for antifouling their paddlewheel/housing? When we got the boat it has the same ablative AF as the hull, and lasted OK with a good blast at 6 knots for 1/2 hr usually being enough to clear if. The AF was flaky and getting a bit thick so I took it all off and coated it from fresh and last season it needed cleaned every two weeks! Wondering if propellor AF might be better or I need a different primer for the plastic?

 

[Minerva]

I don't think I'll sink it. I just really hate letting water get in certain less-accessible parts of the bilge and it occurred to me that an actual valve would do a neat job. A litre in a certain spot is a right nuisance for me.

Sandy, that pipe arrangement sounds like it would functionally work, was it just too cumbersome? I don't think I would have room...

Stemar, I'm imagining that the cock is open when the sensor is in place, with the sensor filling the tube (probably in a machined rod that is an exact fit). Then taking the sensor out to just above the seacock, closing it, and removing it the rest of the way. Not trying to close it on the cable.

If the small amount of water that’s let in -and it really is insignificant, then the solution you’re looking for might be better found in the shape of disposable nappies. Just stick one in the bilge downhill from the transducer to soak up the spillage.

 

[ylop]

I don't think I'll sink it. I just really hate letting water get in certain less-accessible parts of the bilge and it occurred to me that an actual valve would do a neat job. A litre in a certain spot is a right nuisance for me.

I can do it with a lot less than 1L. My intention this year is to cut a big car washing type sponges to have a whole exactly the right size for the transducer pipe (with a slit so it can fitted/removed with the transducer in place). I think that will catch all that escapes and just need a wipe with kitchen roll…

If you were really worried (like that compartment drains somewhere bad) then it would be a lot easier to glass a small “wall” around the sensor (or short length of sewage waste pipe) to the hull to act as a bund that you sponge out than making a custom through hull to fit inside a seacock etc.

 

[Mark-1]

Speed transducers don't seem to be much good when they get fouled. Most (all?) seem to have some arrangement where you can take them out and stop up the hole while you clean them. Many people become just fine doing that, but it is daunting for others, and it rather restricts the transducer to somewhere you don't mind getting wet.

Is there any particular reason why someone can't fit a large seacock to a through-hull, then feed the transducer through it? then it could be withdrawn and the seacock closed while the transducer is still in the pipe, avoiding letting in any water. The transducer would need to be on some kind of fitting to make sure it settled at the right height and was an exact fit, but this is probably simple lathe work. Anything that made it easier to remove would also reduce the need to clean it, since it'd encourage taking it out after each use. (And when I'm not on the boat I'd cap the pipe, so then there's a closed seacock connected to a short straight closed pipe, which is no more concerning than any other seacock)

I've never seen this done, or heard of it. That makes me think there must be a good reason not to do this. What am I missing?

Depending on your skill with fibreglass and the location of the transducer it might be better to make a mini moon pool with an insert which contains the transducer and blocks it off underway.

So essentialy a square dinghy centreboard case with an insert with the 'ducer attached. I've seen that, and it works well.

 

[rogerthebodger]

I looked at fitting a 110 mm PVC pipe coupler that seals with rubber seals fitted over the transducer so a long PVC pipe could be fitted to precent the gush of water in and once the transducer is refitted the 110mm dia long PVC tube can be removed to allow the flooring to be refitted

 

[capnsensible]

Walker log. Problem solved.

 

[justanothersailboat]

Interesting suggestions here, thanks very much everyone. Looks like building a little partition in glass that prevents escapes from getting where I don't want them, might be the winner here.

 

[Daydream believer]

As suggested, Build a bund around the area if you are really that bothered. A 4 inch pipe will fill with water & make it difficult to see the fitting & hard to fit the cap. You suggest that you cannot get water from the bilge, but an oil extractor will do the job in most cases.
A disposable nappy (remove child first) with the elastic removed with a pair of scisors, so it lays flat, will soak up most excess water.
As for antifoul to the paddle wheel I have used Paint
Seems expensive, but is water based, so if one adds some water to the pot & stores upside down to prevent it going off, a good stir will make it last years. Will also do the echo sounder, of course. One only needs a very small application each season & I only clean the paddle wheel mid season, when the boat comes out to wash the Copper coat ( Plus winter of course)I have had my one pot 15 years at least.

 

[captainboo]

The Electradepth was fitted to my boat (not working) so I modified a NASA log to fit the redundant skin fitting. The log could then be retracted and the housing then rotated sealing it off from the water. Never needed to antifoul and could be removed without a drop of water entering the boat. It was a large chunk of bronze though requiring a big hole for fitting! They also did a log version.

 

[Dellquay13]

As for antifoul to the paddle wheel I have used Paint

I found that brand of eco a/f for transducers as effective as a chocolate teapot.
At the same time I used Hempel tiger xtra on the hull, and the only place to get any growth beyond simple slime was on the transducer. It was a 20kt motorboat, so plenty of water flow to self polish, I went back to just using the tiger xtra a/f on the transducer and that worked fine as usual

 

[vyv_cox]

My Airmar combined depth and log has a flap valve in the housing, closing when the transducer is removed. I say 'closing' with tongue somewhat in cheek but it does reduce the inflow considerably.
Velox works pretty well on the log wheel and being so thin has minimal effect on the wheel shape.

 

[justanothersailboat]

I can get water out of the bilge, it's just that it's easy to do so in some places and a complete pain in others! and one of the complete-pain parts is somewhere where it causes problems (and maybe I should carry an emergency nappy). If I ever buy another boat I will look more critically at space access. The bund has the answer here, I have no problem mopping it out.

captainboo, that looks rather like what I was thinking of, only better. Impressive. I imagine these might have been rather expensive originally, which may be why the flap became more prevalent as the "good enough" option.

I found that there is a company selling something very close to what I originally envisaged... with a gate valve, which I tend to associate with undesirable older installations!... at a mindboggling price. Shut Off Valves | A+T Instruments I will never be in the market for one of those, and it also explains why I never saw one, never having been on a "superyacht".

 

[PabloPicasso]

A wide pipe glassed into the hull standing above the waterline would solve it. You could take the sensor out and leave it open & the pipe would only fill to the waterline level, and not flood the boat.

Clean transducer and refit, then just use a pela. Pump to clear the pipe. Perhaps a 4"inch or 6"inch peice of plastic drain pioe would do.

 

[Snowgoose-1]

A wide pipe glassed into the hull standing above the waterline would solve it. You could take the sensor out and leave it open & the pipe would only fill to the waterline level, and not flood the boat.

Clean transducer and refit, then just use a pela. Pump to clear the pipe. Perhaps a 4"inch or 6"inch peice of plastic drain pioe would do.

Yes. A piece of drainpipe would do. Depending on access .

I don't have a problem withdrawing and cleaning. Only a pint perhaps is shipped.

Thread Drift

I've splashed out on one of those electronic logs with no paddle wheel. Yet to be fitted. I should be able to clean it from the pontoon with a deck brush during normal bottom scrubbing. Reviews are encouraging .