speed and depth thru hulls

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Bill Jones

I want to change my older instruments with a Autohelm depth/speed instrument. The location for the knotmeter thru hull is between the second and third sets of keel bolts and about three inches out side of the bilge access hatch on the starboard side. The depth finder used a puck glued to the inside of the hull, located under the mid port side bunk about one foot ahead of the aft end and about four inches out board of the inside wall of the locker.I want to leave the knotmeter thru hull in place and find a different location for the new one. The new thru hull is a smaller diameter hole. The boat is the deep keel version. Bill Jones
 
Dec 2, 1999
15,184
Hunter Vision-36 Rio Vista, CA.
Not a good place for the speed transducer!

Bill: Having the transducer next to the keel is not an idea spot. As the water goes around the keel it will tend to acclerate so you will not get an accurate speed reading. I have the same setup on my H'31. Also the new transducer is smaller than the old one. I am upgrading to a Nexus System 3000. The instruction show that the transducer should be placed forward of the Keel. I do not know your setup but is there room under the v-berth? These instruments recommend that you keep the close to the centerline as possible. If you have not purchased them yet, you may want to get a copy of their installation instructions and see what they recommend.
 
Jan 22, 2003
744
Hunter 25_73-83 Burlington NJ
Thru-hull holes

Mr Dion is right-- speed transducers should be either a foot or more ahead of the keel, close to the centreline, or else far enough behind it to be out of turbulence (like darn near at the transom). Whoever installed the speed thru-hull beside the keel was unaware of this. Even most yards would know better. The depth transducer should also be ahead of the keel, but for different reasons. [wink] --foresight being better than hindsight! Don't be afraid of patching the holes. This can be easily done by laying up a decent layer of Fabmat inside the hull-- make sure you de-wax the surface first, and wash it down with acetone right before sticking the wetted-out mat side down. Let it sag a little into the hole from the inside. Roll it out thoroughly. Then when it's kicked-off go outside and grind off a bit of area around the hole, fill it, and lay up 10-oz cloth over the filler. Later fair in with microballoons or something and repaint the bottom. There should be no significant (or even detectable) loss of rigidity or strength, even so close to the keel. Fibreglass doesn't know as much about 'grain' and so forth as many people think, especially when the adhesion is good. Use a standard hole-saw to drill out your new holes (for a hull with any substantial Kevlar content, be prepared to throw the hole-saw away when you're done). File to fit. 5200 should be good enough as a sealer but there are even better things. Ask a repair yard first. Make sure whatever you use can take bottom paint. JC
 
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