Cut the rudder??

[Jim Cate]

Originally Posted by MicHughV

Jim,
If you were to consider a dam wall, the pressure of the water against the dam wall will be the greatest at the toe of the wall.

This is true, but the density of the water will not be different at the bottom of the dam. For the rudder the difference in hydrostatic pressure at the bottom of the rudder does not change lift, drag or the turning moment generated at any given angle of attack.

As mentioned upthread, the slight lessening of the aspect ratio will slightly reduce rudder efficiency, but again, I doubt if that will be noticeable to the OP in his sailing. A few barnies on the blade will likely have a bigger effect on rudder performance, and we've all suffered from that at times!

Jim

[Fore and Aft]

Geoleo if at all possible, try and make it look like it came from the factory like that. It does not take much creativity to round the edges and put some shape into it. I have surveyed a number of boat rudders that look like my teenage son has just wacked of 4" with a Skilsaw then wrapped some chop strand matt over the wound.
Cheers

[SG]

CHOP OFF?

First, the designer did not put that rudder depth down there for amusement. Our J/160 has a 7’-3” draft to the bottom of the keel and and over a 6’6” draft to the bottom of the rudder. That wasn’t done by accident by Rod Johnstone, either.

Secondly, the center of work, percentage of area of the rudder you might be remove in, and some of the other factors cited in posts above ASSUME you motoring in flat seaway with the boat in a static un-heeled attitude. Maybe in Tampa Bay, a good deal of the time, that probably is the case when the wind isn’t blowing …HOWEVER,

Thirdly, If dont’ motor around all the time in flat water, when you are heeled over in a seaway, the part of the rudder you are cutting off is taking a lot more of the control surface; and, the control surface at that position on the rudder is doing more oork than the top of the rudder. It’s not just 8% is no big deal.

If you dont’ use a spinnake in any wind, never overpower your sail plan, etc., then chop away. I think it’s like: Do you need your two smallest fingers? Not really, except if you try to fully use your hand.

Those are my thoughts.

[Rucksta]

keep the rudder, lengthen the keel

[MGRodems]

I proposed the same question a few years ago for almost the same reasons. My Irwin 43 has a wing keel and a rudder that is almost as deep as the keel. Here is a link to that post.

https://www.cruisersforum.com/forums...er-242770.html

I ended up cutting off about 3-1/2" and the result was quite good. I did not notice any difference in performance. The added benefit is the additional clearance allows you to pivot the boat easier if the wing keel is sitting on the bottom. We ran aground twice since the modification after 4,000 nm (once in the Erie Canal onto gravel at 7 knots and once in soft mud in the Chesapeake while exiting a shallow creek). I hauled out recently and noted the rudder was fine and did not appear to suffer any damage.

When I cut off the bottom of the rudder, I took the piece removed to shape a thick piece of hardwood to insert up into the rudder before glassing over it for the repair. This was to add strength to the bottom of the rudder.

I would go for it.

[Noahr]

Why don’t you call the Beneteau factory/customer support and ask them?

[geoleo]

Originally Posted by Fore and Aft

Geoleo if at all possible, try and make it look like it came from the factory like that. It does not take much creativity to round the edges and put some shape into it. I have surveyed a number of boat rudders that look like my teenage son has just wacked of 4" with a Skilsaw then wrapped some chop strand matt over the wound.
Cheers

I guarantee a polished finished job.

[geoleo]

Originally Posted by SG

CHOP OFF?

First, the designer did not put that rudder depth down there for amusement. Our J/160 has a 7’-3” draft to the bottom of the keel and and over a 6’6” draft to the bottom of the rudder. That wasn’t done by accident by Rod Johnstone, either.

Secondly, the center of work, percentage of area of the rudder you might be remove in, and some of the other factors cited in posts above ASSUME you motoring in flat seaway with the boat in a static un-heeled attitude. Maybe in Tampa Bay, a good deal of the time, that probably is the case when the wind isn’t blowing …HOWEVER,

Thirdly, If dont’ motor around all the time in flat water, when you are heeled over in a seaway, the part of the rudder you are cutting off is taking a lot more of the control surface; and, the control surface at that position on the rudder is doing more oork than the top of the rudder. It’s not just 8% is no big deal.

If you dont’ use a spinnake in any wind, never overpower your sail plan, etc., then chop away. I think it’s like: Do you need your two smallest fingers? Not really, except if you try to fully use your hand.

Those are my thoughts.

Thanks for the advanced advice! Im also thinking that the missing rudder wetted area might possibly add an extra 3.86 knots of speed when Im surfing down those 22.13 foot NE swells!! I tried to contact Rod Johnstone but his Aide de Camp said he was busy for the 'forseeable future'.

[Don C L]

Originally Posted by geoleo

Thanks for the advanced advice! Im also thinking that the missing rudder wetted area might possibly add an extra 3.86 knots of speed when Im surfing down those 22.13 foot NE swells!! I tried to contact Rod Johnstone but his Aide de Camp said he was busy for the 'forseeable future'.

Ha! I’m going to use that one from now on. I’m busy for the foreseeable future everyone!!

[GrayGhosty]

[QUOTE=coopec43;3903135]So instead of having three tangs just have two? Geeez! I'd like to know where the tangs are before I started cutting.

Maybe contact Beneteau or perhaps a cheap stud finder may pick up the welds. (Of course you could use a small drill to locate the tangs,)[/QUOTE

I am not entirely sure if this will work but it might be possible to use a non- magnetic stud finder. The newer ones can tell the difference between metal.wood, plastic ,and iron.. this is. Would allow you to do non-destructive testing. And map. The supporting stucture inside

[RaymondR]

If the bottom of the rudder is about 5' deep, which at 0.43 psi/ft I doubt there is going to be much density increase. 10 mPa is about 1,400 psi.

I'd be inclined to cut it back and glass in a piece of hardwood rather than aluminium.