Hydrovane, how to install it on the OVNI ...

This is a summary of mails exchanged with a UK OVNIst who plan to install an Hydrovane (HV) on the 435 they just bought.
     

Down wind in mid Atlantic

Apologies for the email out of the blue, Will Curry from Hydrovane gave me your address. I have just bought a HV to install on an Ovni. My plan is to have a plate made & attach this to the transom and use H type brackets attached to the plate. Hence trying to keep the transom as free of other supporting arms as possible. My question regards how to fix both plate and the H bracket to the transom. As far as I can see there is no access into the space beneath the transom to enable the use of standard nuts and bolts. Therefore, the options would seem to either drill and tap (possibly using helicoils to reduce corrosion) or cut an inspection plate to enable the use of standard nuts & bolts.

Well, obviously, welding a support on the transom will « screw up » the painting but it seems to be the best option because of how the hydrovane (HV) is built: the plate must be large and vertical and drilling holes in the vertical part of the transom might be a bit dangerous as the twisting effect when the sea is rough could be significant. The HV has its onw ruder and the forces are really big, very different from other models. We did some welding on the transom 2 years ago (Alubat folks did it) for the Watt&Sea support: 1 day for welding, 1 day for the protection layers and first pass of paint and 30 minutes on day 3. If you weld (what I would probably do) you will have to redo the painting 30 to 40 cm around the welded parts as the temperature kills the paint and protection.

     

Nevertheless, as suggested, bolting the support to the transom could be the easiest/fastest option with a support built a bit like on the drawing and then fixed with at least 6 well isolated bolts and nuts plus a lot of sikaflex to ensure the full solution is waterproof. Corrosion is an definitely issue but won't be the only one and to prevent this one you will have to avoid any contact between the aluminium of the hull/transom and the stainless steel bolts. To do this on H2 we used some heat-shrink sleeve around the bolts plus some sikaflex and an isolation paste applied directly on the aluminium of the drilled holes. Looks like belt and braces but we never had any issue taking the HV out of its support. One of the difficulty might be about about having bolts inside the transom as it is closed. As you mentioned, it can be done through an inspection plate. We opened the transom on H2 by cutting a circular a hole in the life raft compartment and adding water-tight cover but this was because we had some water inside due to a 'defective welding' from the shipyard and the rule is « no water in the transom, ever, as it is a sacrificial compartment»

A suivre ...