break away rudder question

[4343]

When using a nylon break away screw, should it be on the top or bottom of rudder??

[fweasel]

The top screw is most often the pivot point, and made from metal. The bottom screw is most often the shear pin and is usually either made from nylon or sometimes brass. Not to say its impossible, but if your shear pin was in the top hole, it would take a tremendous amount of additional force to break the bolt due to the shorter lever arm as compared to using the lower hole.

[NativePaul]

Leave it out and put a spring in, less chance of ripping your transom out, and you almost instantly regain rudder control if it does flip up.

[fweasel]

Leave it out and put a spring in, less chance of ripping your transom out, and you almost instantly regain rudder control if it does flip up.

Interesting idea, and not something I had ever thought of. Do you have any photos of a boat setup like that?

[Shooter]

The spring is a great idea. Only thing I'd worry about is the rudder tilting backwards during a turn.

[NativePaul]

The strength of the spring needed will vary depending on the speed rudder size, rudder thickeness, rudder angle, rudder castor, etc. It would take some considerable trial and error to find the perfect strength if you want to use the lightest spring possible, but such precision isn't needed, even far too strong spring that has no chance of moving under normal use will flip up with a fraction of the impact that it takes to sheer a plastic, brass or alloy sheer bolt, and a flip up a rudder with a tight pivot bolt.

If you want a rule of thumb, we can typically hang out boats from a finger on the rudder just under the spring without the spring giving. Alternatively you could push down on some bathroom scales with the rudder and see how many ilb/feet or N/M it takes to break the sheer bolt and use a spring of the same rating, it will be many times stronger than you need, but you know it will never move in normal use, and poses the same risk to your transom.

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