Drilling My Transom????

[t_dub]

so i've got to drill about a 1" hole through my transom to run the transducer wiring for my new HDS7. was planning on using a cable clam to make it all nice and watertight from the outside, but my question is what would be the best bit to use? the transom is thicker than i initially thought, almost looks like there wood or something sandwiched between the inner and outer aluminum shell???? looks to be about an inch thick. also, once the hole's drilled should i do something to seal the now exposed wood, even though in theory the clam makes it watertight? make sense at all what i'm asking???? fyi, it's a hewescraft searunner, if that makes a difference.

thanks

[Nelly]

Hey 'dub,
I hear you loud and clear! Many aluminum boats use wood in their transoms but it's often less than you imagine.
In other words, what appears to be a very wide span of wood is often no bigger than a 10 or 12 inch width of 3/4" plywood sandwiched between the fore & aft surfaces of the transom.
I'm sure intuitively you see why manufacturers use wood, it's an inexpensive, tough, durable core material that adds stiffness and compression resistance to the engine mounting area.

The hole size you must drill is the size of the transducer wire connector and then we'll seal the hole around the cable by use of a cable gland such as these:

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,

img-9110.jpg (54.28 KiB) Viewed 6115 times

You can find these cable glands at Harbor Marine, West Marine and several other locations.

I would use a hole saw slightly bigger than the transducer cable connector and seal around the gland with Life Calk. If you use 3M 5200 sealant you had better never want to remove that 'ducer!

The Life Calk should take care of the wood within the hole too. Hope that helpa and happy drilling!!!

[t_dub]

thanks for the info and pics Nelly. already got one of those cable glands so sounds like i was heading in the right direction, which is really weird for me do you use that Life Caulk to seal the screw holes for the cable clamps when you're securing the 'ducer cabling along the extended transom or is 5200 a better choice?

also got one other thing to pick you brain about. the two holes in my transom where they ran cabling and the fuel line for my main motor are not watertight, i can see daylight from the inside. not usually a big deal when i'm running cause they are above the swimstep, but if i'm back into some waves, i can definitely see water getting through there, and that happens to be right where my batteries, switch and connections all sit. any suggestions on how to seal up void space around the lines? i was thinking of just taking some spray foam from the inside and filling up the voids. there's a decent amount of volume around the steering and electrical cabling so just running a couple beads of silicone caulk won't do it.

[Nelly]

Yo Dubby,
I love 3M 5200 Marine Sealant but it is a bugger to remove if you ever have to service the area that you've sealed with it!
That said, I would definitely recommend it for sealing screw holes for your cable clamps. 5200 will hold a screw very well and is fairly easy to work with in that application.

To your question on engine cables and fuel lines, I definitely would not use 5200 or foam. Fuel lines often need to be replaced as do engine cables so you need to use a "split boot".

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Since the boot is split, you can install it without disconnecting your engine cables and fuel lines and while not completely water tight it will shed 95% of the water that splashes up to it. The situation you described with salt water dripping on your live electrical is not healthy. Salt water absolutely loves to eat wires with electricity flowing through them and your battery and terminal connections will not stand a chance in that environment.

Dry electrical systems are happy electrical systems and the more water you can exclude from your boat, the less maintenance you'll have to do!