A Rudder size Problem.

[old_salt]

Can any one help with a rudder problem.
I am with a pal completely refitting a 30 ft G.U. Laws designed 1905 Traditional Counter sterned Gaff Cutter just about replaced every thing bar 90% of the planks, keel, hog and the 5 main oak floors. We have been at her off & on since 1989. But she is getting there now and hopefully another 6 months or so Ha Ha will see her in the water. She had an engine fitted about 1947 and the rudder opened up with a cut out for the prop. We do not have the original rudder only a replacement. We are making a new rudder on the out line of the original with a little bit added based on that we can take some off but if it is to Small very difficult to put on and wish to retain the prop though the stern post. We have a line drawing from one of F.B.Cookes books "Cruising Hints" showing the the original rudder outline.
Now my question is do we make the rudder bigger in area to compensate for the cut out or not and is there any specific ratio applicable to ruder sizing and what effect will an over or under sized rudder with a big hole in have when under sail. Many thanks in anticipation of any help. I do have some more requests but I will put them on another post.

 

[johnlilley]

For what it is worth, the cut out does reduce the power of the rudder so the less cut out you have , the better, even if it means dropping a removable section in this part if that was possible. By just increasing the width it will likely give heavier but not especially more positive steering, loading the fittings even more (like steering a dinghy with the rudder lifted) Better to increase the area close to the base and lead of the rudder. If the old rudder is conventional ellipse shape, fill in the area deep down and contemplate using straight trailing edge with the widest part lowest down but keeping the overall width less than the maximum width at present. The most power is produced from deep water and close to the leading edge. Look at Cutty Sark, very narrow but very deep. Just a thought. Regards John Lilley

 

[Peterduck]

I concur with John Lilley's comments. In addition, I would like to add that you'll need a gap around the prop enough to give a 1" clearance between rudder and prop blades. What is possibly of more effect than simple rudder area is the Aspect Ratio, or the ratio between height and width. A fast yacht will need a slim rudder, with an aspect ratio of about 4 or 5:1. A Folkboat is a good example of this. My old ex-fishing boat has a low ratio rudder, about 2:1. This was good for greater control when dragging a net at 1-2 knots, but is terribly heavy at 4 knots. It's a real effort to tack at speed, even with wheel steering.
Peter.

 

[Mirelle]

Probably not a very helpful answer...

I'm intrigued! The only Laws boat that I can think of that is illustrated with line drawings in "Cruising Hints" is "Nereid II", but she is a canoe sterned yawl. Tell us more!

My very definite advice is to avoid making a cut out in the rudder for the prop. Far better if all the cut out is in the deadwood or if that is impractical for structural reasons then an offset prop is better.

The damage done to the steering and handling under sail by having more than 50% of the cut out in the rudder is very serious. A well mannered boat can be turned into an absolute swine.

 

[old_salt]

Re: Probably not a very helpful answer...

[ QUOTE ]
I'm intrigued! The only Laws boat that I can think of that is illustrated with line drawings in "Cruising Hints" is "Nereid II", but she is a canoe sterned yawl. Tell us more! [ QUOTE ]


The yacht is Mercia III she is featured in the Third Edition of "Cruising hints" what edition is Nereid II in? I have editions 3 to 6. and looking for editions 1 & 2. I am intending to put a post all about Mercia III with requests of help with info when I understand how to post photos but maybe I should just bite the bullet and do the post the pics can come later. The Rudder situation is she had an engine fitted in 1966 we have made a new "over sized" rudder and have retained the prop shaft through a new Stern post due to engine room so the rudder cut out has to be. and it is the profile that concerned us hopefully the new one has sufficient to remove the unwanted area..

 

[Mirelle]

Re: Probably not a very helpful answer...

I can't work out how to post photos either!

I'll check my copy when I get home, and report back. I remember noticing "Nereid II" because I knew her as a boy, when gentleman named Newman owned her, in Walton. The only other thing that I can remember about GU Laws was that he was killed in WW1; a very talented designer, but you already know that.

 

[cliffordpope]

Re: Probably not a very helpful answer...

I don't think the analogy with the Cutty Sark tells the full story. Yes, she has a very deep narrow rudder, but it is also tiny in size relative to the length of the ship.
Compare that with a dinghy rudder, which is about 10% of the boat's length.
Isn't the difference that steering a big clipper was largely a matter of sail balance, whereas sail balance in a small boat is almost totally ignored. Steering a dinghy is by brute force on the tiller - let go and the boat instantly spins up into the wind. In between those two extremes come ordinary yachts, which ideally have the rig so balanced that they will steer a straight course with minimal touch on the helm.
Surely the better-balanced the sail plan, the smaller the rudder area needs to be?

 

[old_salt]

Re: Probably not a very helpful answer...

Here is an article on G.U.Laws and the Restoration of "Tarifa" Classic Boat November 2001 edition 161.
Doe's any one have any other information about G.U.Laws and is there any one else with a Laws boat.

 

[Mirelle]

Re: Probably not a very helpful answer...

My mistake. Nereid (without the II, which she has alway had, is in "Weekend Yachting" and I have the second edition.

I glanced through my 1977 Lloyds Register and there are a goodly number of Laws boats listed. The ECODS, of course ("Chittabob", etc) several cruiser a six metre named "Gybo" (!) but oddly enough "Mercia III" is not shown. (mind you, they also manage to omit the Deben Yacht Club from their list of UK yacht clubs...)

 

[old_salt]

Re: Probably not a very helpful answer...

Hi Mirelle. Mercia III was fully listed in Lloyd's from 1905 to the last entry I know of 1970. I have a number of F.B.Cookes books. The the second edition you refer to is it "Cruising Hints" or "Weekend Yachting" I have an edition of "Weekend Yachting" dated 1933. It would appear from the written work of F.B.C. that he and G.U.Laws where well known to each other and must have worked together at some time. My research of records show G.U.Laws designed some 55 or more yachts from canoes to the 43 ton "Wayfarer".

 

[Mirelle]

Re: Probably not a very helpful answer...

Sorry, my fault. Second edition of "Weekend Yachting". I only run to four Cookes, so far, though I do quietly pick them up in secondhand shops when I see them.

I wish I still had the copy of YM, from the late 60's, which contains the article he wrote when he was 100. It was a two page paean to the merits of East Coast Mud! I do have the article on gaff topsails from a year or two before that.

I have the oddest impression that my potters around the east coast are always accompanied by two ghostly presences, quietly muttering advice and reproach. One is my late father, and the other is FB Cooke.

I would like to see a proper article on Laws. Any chance you will send one in to CB?

 

[old_salt]

Re: Probably not a very helpful answer...

There is an excellent article about G.U.Laws in CB November 2001 edt 161 by John Leather ( From helm to drawing board) a back copy enquiry may get you one it did me. If not PM me and I will email you a copy.

 

[old_salt]

Thank You to all who replied your help and comments are very much appreciated. I am working on a request for information on G.U.Laws and Mercia III hopefully with photos.
Again Many Thanks.