Model Boat Mayhem

Dry Dock / Shipyard: Builds & Questions => Yachts and Sail => Topic started by: Rogirby on July 04, 2011, 01:42:54 PM

Title: Rudders - size or movement
Post by: Rogirby on July 04, 2011, 01:42:54 PM
Had first test sail after fitting RC to my 55 year old marblehead. There does not seem to be enough effect from rudder movement - whilst running it clearly has some effect but when close-hauled it does not seem to do much at all.
I am trying avoid doing anything which affects the original deck fittings arrangements - e.g. no new holes drilled in the deck etc - so my options for how I set thing up are a bit limited.

The question is which is the best area to experiment with - increase the amount of rudder movement by adding a block arrangement to the rudder arm control lines or increase the rudder size by making a removable extension (vertical or horizontal?)?

The present rudder is a skeg approx 3.5" deep and 2 inches wide.

Any thoughts would be appreciated
Title: Re: Rudders - size or movement
Post by: rmaddock on July 04, 2011, 02:40:22 PM
That does sound quite small as rudders go. My marblehead's not here in the college library so I can't check but it's bigger than that. Some boats have a "display" rudder which is more "scale" looking. Perhaps you've got one of these?
Title: Re: Rudders - size or movement
Post by: Netleyned on July 04, 2011, 04:03:29 PM
Just run the rule over my M rudder
7Inches by 3 longest and widest points

Ned
Title: Re: Rudders - size or movement
Post by: Brooks on July 05, 2011, 01:18:02 AM
With wings, long span with narrow chord are more efficient (lift vs drag), so a deep, narrow chord rudder would be good for racing. But the same area oriented horizontally (that is, a shallow, wide chord rudder) will work much better for sculling. So, the question becomes: is your sailing pond beset by calm, fluky winds =>sculling rudder to get you home , or are you more interested in racing =>efficient rudder?

I put the sculling type rudder on my square riggers as I find myself sculling more often than racing :-). My ships already move faster than scale speeds, so I don't usually need the greater efficiency of a racing rudder.

Rudder swing of 45deg to either side of neutral should be sufficient. This is within the normal servo arc, and will be achieved at the rudder if the servo arm and rudder arm have equal lengths.
Title: Re: Rudders - size or movement
Post by: tigertiger on July 05, 2011, 02:09:07 AM
Are rudder sizes governed by the class? If so it will be on a website somewhere.

If the rudder is class size, then the problem could be with your sail setting.

Just some thoughts
Title: Re: Rudders - size or movement
Post by: tony23 on July 05, 2011, 08:24:02 PM
the maiximum throw on your rudder should be about 30mm either side or 50 degrees anything more and it will act like a brake, Marbleheads have long (7inch+) thin rudders because they sail very leaned over into wind anything shorter and the rudder is not in the water.
Title: Re: Rudders - size or movement
Post by: malcolmfrary on July 05, 2011, 08:44:17 PM
55 year old Marblehead.  Maybe not originally a radio boat?  If so, the rudder was not for steering, it was for trimming it to sail straight.  A radio boat, needing to steer, will benefit from a larger rudder.
Title: Re: Rudders - size or movement
Post by: tobyker on July 05, 2011, 09:28:19 PM
Don't some of the modern racing yachts have twin rudders so one is vertical when the boat is heeled?
Title: Re: Rudders - size or movement
Post by: knoby on July 05, 2011, 10:37:08 PM
measured my rudder tonight, its 8 x 3 inches. & it turns about 45 degrees

Glenn
Title: Re: Rudders - size or movement
Post by: rmaddock on July 06, 2011, 09:10:16 AM
Given it's age and the suggestion that it might not have been an RC yacht. It's also possible that the rigging is set up for stability in a straight line....I think that'd have something to do with mast step position. That could be fighting you in the turn too.
Title: Re: Rudders - size or movement
Post by: Rogirby on July 06, 2011, 10:29:35 AM
Thanks for many useful comments which give me some things to work on.

By the way - when she was built it was designed for free sailing with braine or vane steering gear so, yes, the thought that it was probably designed for fairly small adjustments and straight sailing is probably right.  (Incidentally, the design is "Windsong" which I think was quite well known at the time she was built)

Now to start work on some way of fitting a removable rudder extension!