input on replacing knot meter and depth sounder on Caliber 28

[lk240]

Hello,

I'm starting to plan replacement of the knot meter and depth sounder on my 1986 Caliber 28. I purchased the boat in late 2018 and when I splashed in spring of 2019, there was a small leak around the depth sounder and as you can see from the pic it has been treated with a copious amount of Life Caulk over the past few years which stopped the leak but I would like to fix it for good this time.

I would be interested in opinions on the best approach to doing this as I'm just learning about all the various options and how I would go about removing the current units and best options for replacement units. thanks for your consideration.

Lisle

[psk125]

It will be less work to replace the old units with ones that are the same size. If the leak has stopped and they still function, it would be even less work to leave them alone and go sailing.

[lk240]

good advice, thanks.

[Northbound44]

My opinion is, remove the old thru hull by using one big bolt , nut ,two big washer and two piece of wood. By screwing the nut, you will extract it without damaging it.
Clean the thru hull and inspect it for crack or damage, replace as needed the defective part and reinstall with bedding. Replace the O rings on the sounder plug, lubricate with silicone grease, install and test. That’s all.
Good luck

[lk240]

thanks for the reply!

[CarinaPDX]

Some thoughts:

You will need to remove the current transducer. Either you can clean the transducer and the hole thoroughly with sandpaper and acetone, and re-bed the transducer, or put in a new transducer after cleaning the hole.

Plastic transducers, or anything else (like Plexiglas windows) can be attacked by some chemicals. Specifically, the original LifeCaulk was a polysulfide sealant and was not to be used. It was also a very poor sealant with a short life. Today there are at least some (maybe all) LifeCaulk products that are not polysulfides. So check to see that the sealant you are using is not a polysulfide. Polyurethanes (5200, Sikaflex) do a great job - just likely to be too great: removal is often destructive. Still, they are the best, so if you use one of them then just seal the flange and not up the threads. I would never use a silicone sealant below the water line. Most marine sealants will indicate whether they are to be used below the waterline so have a look.

You might consider replacing the transducer with a newer one if you are thinking about upgrading other electronics. What you have is most likely an analog transducer with a proprietary plug to the back of a dedicated display. A modern system would have a "smart" digital transducer attached to an NMEA 2000 backbone linking a chartplotter and other displays and sensors. This design provides for many synergies, at a price. OTOH if it ain't broke don't fix it. If you're happy with what you have then just clean it up and slap it back in

Greg

[lk240]

Very helpful, sincere thanks.

[roverhi]

Originally Posted by CarinaPDX

Some thoughts:

Plastic transducers, or anything else (like Plexiglas windows) can be attacked by some chemicals. Specifically, the original LifeCaulk was a polysulfide sealant and was not to be used. It was also a very poor sealant with a short life. Today there are at least some (maybe all) LifeCaulk products that are not polysulfides. So check to see that the sealant you are using is not a polysulfide. Polyurethanes (5200, Sikaflex) do a great job - just likely to be too great: removal is often destructive. Still, they are the best, so if you use one of them then just seal the flange and not up the threads. I would never use a silicone sealant below the water line. Most marine sealants will indicate whether they are to be used below the waterline so have a look.

Greg

A few plastics, Beckson Port's plastic frames not the clear plastic comes to mind, don't get along with poyurethane or polysulfide sealants. Would bet that there are no through hulls or other below the water line plastic fittings that are effected by either of those types of sealants.

I've been using LifeCaulk for more than 50 years and have never had a problem with any fitting that was bedded properly. Have pulled up 30 year old fittings and the sealant is still pliable, thoroughly bonded to the substructure and working just fine. One of the biggest advantages is LifeCaulk doesn't seem to go off in an opened tube as the polysulfide sealants. Pisses me off when I'd go to bed a fitting and find a six month old tube of caulk other than LifeCaulk that has gone off in the tube and had to be thrown away. Much prefer LifeCaulk (polysulfide) to polyurethane as far as ease of use. Its easier to clean up with mineral spirits and just seems to be better to work with. Both LifeCaulk and polyurethanes have adhesive qualities but have been able to pull fittings up with a steady pressure easier than with polyurethanes and forget it completely with 3M 5200.

The only way to fix the leak is pull the fittings and rebed properly. No way would I live with a leak that was stopped by sealing from the inside. To be safe it needs to sealed from the outside. The knot meter sender should be an easy removal, pull the transducer, undo the clamp nut, strip off as much of the old caulk as you can, apply steady pressure possibly by standing on it, and it will eventually pop free. The Depth Sounder transducer is a bit more of a problem because the wires limit your ability to apply pressure to push it out. Possibly fastening a couple of battens to a board so you aren't crimping the wire while you apply pressure may be possible. Just did the above last haul out on the knot meter and depth sounder though hulls.

Have fun getting the job done with as little Boat Yoga as possible.

[Yellowjacket]

I'm replacing my old water speed indicator (B&G) with a new DST800. The new unit will provide waterspeed, depth and temperature to a NMEA 2000 network, allowing me many options for display.

The old B&G was very robust except for the paddle wheel, and had a great handle for removal. The new unit may be a little more delicate to remove during extended stays on the mooring ball. Almost every DST800 you can buy — Furuno, B&G, Raymarine, etc is made by Airmar.

The old unit went through a 1 7/8 inch through-hull, the new one is 2 inches. Therefore, the through-hull hole has to be enlarged. Removing the old will take some force and/or some heat.

I enlarged a through-hull on a friend's boat, though his was solid glass. The best results were with a semicircular file and spending some time after marking the new diameter. On his boat I coated the newly exposed glass with epoxy to prevent water intrusion, and will do the same on mine.

Then bed with Sikaflex or 5200 (or the next step down, 4800? to make future removal less strenuous).

[lk240]

thanks roverhi and Yellowjacket, very helpful replies.

[lk240]

Progress update. I spent about 2 hours scraping off the life calk. I found my hose removal tool very helpful getting the life calk out from under the wide lip of the DataMarine depth sounder, it penetrated the caulk and I could pull out larger sections.

sprayed a little PB Blaster around the locking nuts and after 1 day was able to get the locking nuts off both thru hulls, thankfully.

The knot meter thru hull was slightly loose, I can turn it slightly about 3/4 inch each way. The depth meter thru hull is not budging so planning to try some Life Calk Release and crafting the wooden block/long bolt approach to try and get them out.

I'm now looking through the options for replacement transducers and I'm leaning toward upgrading speed, depth, and wind indicators with a modern system, NMEA 2000. The current wind system is an old Stowe unit that does not work.

I like the Garmin GNX wired all in one package but the transducers are 43 mm and I need 2 inches. Would be great to do the DST800 but I am inclined to go with 2 transducers rather than 1 and try to glass over the other hole. Curious if one option would be to go with the DST800 and then find another thru hull to bed and just plug the hole.

[CarinaPDX]

The great majority of thru-hull transducers are made by Airmar. They have a wide choice of depth-only, speed+temp-only, and depth+speed+temp transducers, many of them with NMEA 2000 interfaces. Some of the newer ones use ultrasound instead of a paddlewheel for measuring the speed - for those with more money to spend. See: Product Information | AIRMAR Transducers

Greg

[lk240]

Thanks!

[lk240]

Progress update 2: I crafted the wooden block and bolt tool and it worked like a charm! Got both thru hull fittings out without damage. Turns out one hole is 2" 1/8 with a chamfer and the other is 2" with no chamfer but it looks like some of the fiberglass 1/2" around has been removed to create an indentation of sorts. now I need to track down a thru hull that will fit the larger hole.

[lk240]

Progress update 3: I've decided on a Garmin package with GMI20, gwind, and the DST800 that will go in the old depth sounder hole. SR Mariner still sells the thru hull fittings and dummy plugs for the old knot meter so I will replace the old knot meter thru hull because the hole is 2-1/8" and I've been unable to find another thru hull fitting that size with an appropriate transducer or plug.

I'm still thinking through the issue of how best to prep the thru hull holes. the 2-1/8" hole feels slightly loose with the thru hull inserted and there is I a 1/4" gap on the outside of the hull around the flange of the hole where the DST800 will go where the hole was bored in around 1/8 with 3" diameter.

In searching the archives I found this post I think is relevant about using epoxy to help fill a gap of this sort in this situation, also to help protect the hull from delamination using just sealant.

https://www.cruisersforum.com/forums...ize-30958.html

Planning to play with some epoxy and see if this is something I could do.

also planning to go with 3M 4200 as the sealant.