Size matters

[Guest]

I plan to replace a log and echosounder soon that will involve through-hull fittings.
My present log transducer paddlewheel (an Incastec) goes through a 45mm hole. I plan to replace it with a Silva that requires a 43mm hole. Can the difference be safely filled with Sikaflex or something like that or should I glass the old hole shut and make a new one?

Also, the echosounder transducer comes with a through-hull option as well as a, well, well. Does going through-hull make a lot of difference?

Lastly, I've never gone through a hull before, so any tips (other than take the boat off the water)?

I know that's a lot of questions, but, from what I've seen, lots of people seem to enjoy answering them.

Thanks in advance

Deepest Regards

Jonah

 

[yoda]

Cutting holes to within 2mm is quite an art unless you use good hole cutters. Does the new hull fitting have a large flange and backing nut that would take up the difference with some sealent in there? You will probably only know when you remove the old fitting just how big the hole is. I would expect the new fitting to have enough of a lip however to just use the existing hole. If you can't fit the new skin fitting in the existing hole glassing it up is quite a job so you may be better making up a washer shaped plate of brass that can be fixed to the hull independant of the skin fitting with the transducer fitted to that. I don't like making more holes in the hull than is absolutely necessary. Lots of posts on fitting echo sounder transducers through hull or internally and my reading of all I have seen is that it depends on the echo sounder and your hull. For what it's worth, mine is a plastimo and works well fitted internally in a salt water bath.

 

[rogerm]

My comments are similar to Yodas. I would certainly prefer to adapt the existing hole rather than fill in the old and make a new since then you have two weak spots and for 2mm the difference is minor. You will have to use Silkaflex or similar for bedding in anycase. Might as well use it to fill the gap and as Yoda says it is difficult to make a precise hole with a hole saw. The saw tends to wander a bit especially in the initial stages so you need lots of sealer to make sure it is tight but in anycase the flange on these are relatively enormous.

As far as the sounder goes I think the consensus is that it reduces the sensitivity a bit having them internal but that said it hardly makes any difference for normal use. They are all self adapting so it is unlikely you will notice the difference. Mine is internal and has to work down through the shallow keel (I have a cat) and I have never had a problem believing the figures it gives me. In fact now that I have a fishfinder as well which is fitted to the lower edge of the transom ie external, I can tell you that the depth figures are always the same within 0.1m.
Roger