Haul-Out Tuesday: Looking For Ideas On My Old Thru-Hulls & Transducers?

[testingthewaters91]

Hauling out Tuesday and could use some advice.

I’ve got two thru-hulls in my boat’s bilge area:

One is a depth transducer that still works fine.

The other is a speed transducer/paddlewheel that barely works anymore.

Both thru-hulls have slow leaks, and the backing plates underneath are rotted and soft. I’m going on the hard, so I’ll have time to fix it properly.

I’m debating whether to:

Just re-bed the same depth transducer after fixing the hull and backing plate.

Upgrade to newer transducers for depth or speed.

Glass over the holes completely if I decide I don’t really need these thru-hulls anymore.

I don’t think I need new seacocks in those spots for anything else, and I’d prefer fewer holes in the boat if possible.

My questions:
Would you keep the old depth transducer if it’s still working, or replace it while the boat’s hauled out?

Is a thru-hull speed transducer worth keeping, or should I rely on GPS?

If I remove them, would you glass over the holes completely, or leave them as spare seacocks just in case?

Any tips for repairing the hull/core if it’s wet around those holes?

Trying to keep the boat simple and avoid future leaks. Appreciate any thoughts or experiences. Thanks!

 

[Davidasailor26]

What kind of instruments are connected to the transducers, and what kind of condition are they in? If you upgrade the transducers there’s a good chance you’ll need to upgrade to NMEA based instruments, which could start to get expensive.

You could get an in-hull depth transducer and reduce one thru hull that way.

On the Chesapeake there is some current so it’s nice to know speed through the water. I don’t know if I’d call that critical.

Any tips for repairing the hull/core if it’s wet around those holes?

Most boats don’t have cored hulls, especially below the waterline. So there’s probably nothing there other than fiberglass that you can either reuse for the new thru hull, or you could just bevel around the areas and patch with fiberglass and epoxy if you’re not reusing them.

 

[Tally Ho]

Upgrading transducers may not be as easy as just changing the transducers. For example, I have a very old transducer for a speed display that isn’t made any more. So if I put in a new transducer, I will also need a new display.

Do you know what sort of instruments your new boat has? Do you have a Chart plotter? If so, a new transducer upgrade may interface with a chart plotter. For instance, if you bought a speed/depth/temp transducer that uses NMEA2K, you could read all of that data on a NMEA2K chart plotter.

Do you have an auto pilot? Wind instrument? VHF? AIS receiver? Chart Plotter?

You should really have a depth reading. You could use GPS for speed, BUT if you are in areas with currents, tides, etc. you could really use the speed transducer to see speed over ground vs speed through the water.

You should plan, at a minimum, to remove the transducers, replace the backing plates (fiberglass, G10, or even epoxied plywood), and rebed them with new sealant. If any of them are leaking through the transducer, it probably needs to be replaced or eliminated.

An instrument upgrade may be in order, but it won’t be cheap. I would do an inventory of what electronics you have, what works and what doesn’t, and then determine what upgrades you have $$ for.


Greg

 

[testingthewaters91]

I’m considering glassing over the old transducer holes in my hull. My current transducer technically works, but it's leaking, and the knot meter is practically useless once barnacles grow—it stops spinning and freezes up.

I’m leaning toward relying on GPS for speed and possibly depth. Is there any way to get reliable depth readings without installing another through-hull? Like a transducer I could mount inside the hull or somewhere else?

How do you guys keep your paddlewheel knot meters working long-term? Mine seems hopeless with marine growth.

 

[kappykaplan]

Is there any way to get reliable depth readings without installing another through-hull? Like a transducer I could mount inside the hull or somewhere else?

Yes, as Davidasailor26 said yesterday. Search for "in hull depth transducer".

 

[testingthewaters91]

Yes, as Davidasailor26 said yesterday. Search for "in hull depth transducer".

Excellent. I see. So glassing over the holes will be the best bet. Later I can upgrade to an in hull transducer.

 

[BigEasy]

How do you guys keep your paddlewheel knot meters working long-term? Mine seems hopeless with marine growth.

At one time I coated the paddle wheel with anti fouling paint, being careful to ensure that the wheel continue to spin. Still had to remove it periodically to clean it.
Now I mainly leave the blanking plug in place & use data off the chart plotter when day sailing. If I plan a weekend trip, I will install the paddle wheel. Also, on haulout, I remove the depth & speed transducers to avoid damage from lifting straps & overly aggressive sanding of the bottom.

 

[kappykaplan]

How do you guys keep your paddlewheel knot meters working long-term?

I take mine out and install the blanking plug at the end of the weekend - part of putting the boat to bed for the week.

 

[testingthewaters91]

Lots of excellent ideas in this thread so far—really appreciate all the input.

I totally agree that using the blank plug when the paddlewheel isn’t needed is a great idea. I’m planning to do the same.

Quick question: On my boat, I’ve noticed that one of my paddlewheel transducers looks quite a bit newer and in better shape than the other, even though they appear very similar. I’m going to pull them both out and measure them to confirm.

A previous poster mentioned that if one of these is leaking, it probably needs to be replaced outright. I’m not sure I fully agree—couldn’t it just be an old O-ring that needs replacing?

I’m planning to take both transducers out and inspect them carefully. Is there anything specific I should look for that would indicate it’s time to buy new units instead of just servicing the existing ones?

Also, if I decide to keep them, I was thinking of backing them with G10 and bedding them in 5200 to make sure everything stays strong and watertight. I feel pretty confident that would hold up for at least five years or so.

Is there any reason to think the transducer housing itself might pose a risk of failure or leaks while offshore—even if it appears in good shape?

Thanks a ton for all the help so far!

 

[BigEasy]

Remove & check the O ring(s) to determine if cracked or split; that could definitely cause a leak. I coat the O ring with synthetic grease or KY to keep them lubricated. G10 or epoxy coated plywood is fine for backing plates & if bedded with 5200 should last the remaining life of the boat! I wouldn’t use 5200 on the transducer thru hull. Guess that it is possible that the internal part of transducer could develop a leak; however, you have the blank plugs that can be used if necessary. I once changed depth & speed transducers when converting from old & obsolete instruments to new instruments that included replacement transducers.

 

[testingthewaters91]

Remove & check the O ring(s) to determine if cracked or split; that could definitely cause a leak. I coat the O ring with synthetic grease or KY to keep them lubricated. G10 or epoxy coated plywood is fine for backing plates & if bedded with 5200 should last the remaining life of the boat! I wouldn’t use 5200 on the transducer thru hull. Guess that it is possible that the internal part of transducer could develop a leak; however, you have the blank plugs that can be used if necessary. I once changed depth & speed transducers when converting from old & obsolete instruments to new instruments that included replacement transducers.

I honestly don't know if the previous owner kept the blank plugs. I have not seen them.

 

[BigEasy]

If you replace the instruments, you will likely need to replace the transducers also. The manufacturer usually includes a blanking plug in the kit. If you keep your present setup, determine the instrument manufacturer & model number and order a blanking plug from Defender, West, etc or try purchasing from EBay. If a common manufacturer such as Raymarine, Garmin, etc., Airmar usually supplies the transducer, so you should be able to purchase a blanking plug from them. Should have one onboard in event of an emergency Or for occasional cleaning of the real transducer. They are relatively inexpensive.l

 

[testingthewaters91]

If you replace the instruments, you will likely need to replace the transducers also. The manufacturer usually includes a blanking plug in the kit. If you keep your present setup, determine the instrument manufacturer & model number and order a blanking plug from Defender, West, etc or try purchasing from EBay. If a common manufacturer such as Raymarine, Garmin, etc., Airmar usually supplies the transducer, so you should be able to purchase a blanking plug from them. Should have one onboard in event of an emergency Or for occasional cleaning of the real transducer. They are relatively inexpensive.l

I continue to be astounded by the lack of care and proper procedure undertaken by the previous owners of this boat. It seems like every time I fix one issue, I uncover evidence of shortcuts or questionable repairs. Thanks again for everyone’s help as I sort this out!

 

[testingthewaters91]

Hi everyone,

After some discussion, thought, and reflection, I’ve decided that my paddle wheel and transducer are useful for how I sail.

Now I’m trying to figure out: how can I tell if my current equipment is still worth keeping and safe to keep in service?

Are there specific checks, tests, or signs of wear I should look for to decide if it’s time to replace them? Or is it more a matter of age and peace of mind?

Thanks for any advice from folks who’ve been through this decision!

 

[kappykaplan]

After some discussion, thought, and reflection, I’ve decided that my paddle wheel and transducer are useful for how I sail.

Now I’m trying to figure out: how can I tell if my current equipment is still worth keeping and safe to keep in service?

What brand? Photos of the display heads? Photos of the paddlewheel and transducer?

 

[testingthewaters91]

What brand? Photos of the display heads? Photos of the paddlewheel and transducer?

Here are the display heads for the transducer and the paddle wheel. The knotmeter display reads a bit questionably, though I haven’t quite pinned down the issue yet. It might work fine, or it might not. When I was out sailing, it was showing some strange readings, though to be fair, one of my friends was fiddling with one of the dials back and forth, so that could have thrown things off.

The transducer depth display, on the other hand, seems to read quite accurately, from everything I’ve seen so far. It’s been reliable out on the water.

For what it’s worth, the knotmeter display is an SR Mariner, and the transducer depth display is Hummingbird.