Ketch/Yawl Handling

[fer@fer]

Hi Jeff.

If you are still awake, and really want to read the 5 chapter discussion on scetch, you can just copy the first sentence of the mentioned post, which reads
Quote
As was found during the model tests and also the V.P.P runs, the heel angle of the vessel is critical to the performance. Since in section 4.2 it has been specified that a reduction in the keel length is necessary, if the same rig with the same sail area is carried on the new yacht she will heel to a greater angle as the righting moment is reduced
Unquote

Paste it in google, and two occurrences appears. The first, is this thread, the second, the UK page.

Regards

[Joseph Hardin]

The link worked for me, and they are talking about both models and scaled up versions, so that may be the source of some of the confusion. No mention of "scetches" there though :-)

Here's the intro that gives the context:
SYNOPSIS

The current development trends for both model and full size yachts are discussed, and related to each other. The advanced development in the model field concentrating mainly on the Radio Marblehead class is explained, and the sailing performance of the models is examined. A test model fitting the RM class is produced and its design and construction process is explained. The sailing performance of the test model is analysed, and critical areas are established.

The test model is then scaled to full size and a wider model hull form is also scaled up, so a comparison can be established. The performance of the full size yachts are analysed using a V.P.P and a comparison between the two yachts is made. Other aspects of design such as motion and structural design are then looked at, and related back to the two different hull forms.

The hull and appendages of the scaled up models are then modified with regard to the previous sections, and values for keel length and sail area are looked at. The length of the vessel is considered with respect to accommodation and crew size. The application of the vessel is also considered and racing classes are looked at, and suitable classes are discussed.

HTH,
Joseph

[T34C]

All of the post so far have assumed that a ketch, or more specificaly a yawl, has a ruduced amount of sail area flying from the main mast. That the sail area was divided among two mast instead of one. What about the various models of boats that came in both sloop and yawl variations with NO change in the main mast or its sail area but simply added sail area with the addition of the mizzen mast?

[Tartan34C]

Originally Posted by T34C

All of the post so far have assumed that a ketch, or more specificaly a yawl, has a ruduced amount of sail area flying from the main mast. That the sail area was divided among two mast instead of one. What about the various models of boats that came in both sloop and yawl variations with NO change in the main mast or its sail area but simply added sail area with the addition of the mizzen mast?

You have the yawl rigged version of the Tartan 34C and that may not be a good example for this question. By adding the mizzen you are moving the center of effort for the sailplan aft but you can still have a balanced 34C by just not putting the centerboard down all the way. Most boats don’t have a centerboard so you can’t just add the mizzen without some other changes. I know that there must be an example of a boat designed without a center board but has the option of adding a mizzen and I can’t think of one offhand. All the examples I can think of that add the mizzen change something in the design to allow for the movement in the center of effort of the sailplan.

It’s an interesting question and if you could think of an example I would like to look into it and see what they did to maintain the balance of the boat.

By the way I have the drawings for the 34C from S&S and I put them into the software we use for design and analyzed the hydrodynamics and balance because it’s the boat I own and I will probably add the mizzen so I wanted to see what effect it had on the boat. I also wanted to check the rig using FEA software and determine the strain in the rig before deciding on upgrades.
All the best,
Robert Gainer

[T34C]

I may be wrong, but I think the Alberg 37 came in both yawl and sloop with the same main mast sail plan. This might be an interesting example because I believe most of the factory A37 yawls have had the mizzen removed to convert back to a sloop.

[Tartan34C]

The Alberg 37 had a different main in the sloop and yawl configuration. Also I think she didn’t work out as a yawl so a lot of them were converted back to sloops. She is sort of an example that proves the rule that just adding a mizzen and shorting the main boom without MOVING the main mast doesn’t work.
All the best,
Robert Gainer

[werebeagle]

So, if I understand correcty, the boom on the yawl version of the T34C is the same length as the Sloop version?

Charlie

[T34C]

The Tartan 34C did come with several diferent boom lenghts, but the short answer to your question is yes. My 34C Yawl has the same boom length as Roberts "Tartan 34C", 34C sloop. I don't know if the yawl was an experiment that was tried when they made the decision to shorten the boom, there weren't very many factory yawls (less than 5%)

I have to think there are other examples out there of a sloop/yawl option with the same main mast sail plan, especially of that era.

[pigslo]

My boat, the Heritage West indies was offered as a sloop, ketch or cutter. I ran across onn built as a cutter but none built as a ketch. The foot of the main on the sloop is 14'6" and the ketch is 11'6". That is the only difference
I can see on the sailplan as I have the original prints.
pigslo

[dbraymer]

Well, I bought your problematic boat.
The CT 47 Tall mast has the sloop (actually cutter) main mast, and then it has a moderate sized mizzen, on top of a very modern Kaufmann Ladd under body. 38 foot lwl and about 30,000 lbs.

The small mizzen looked pretty much undisturbed and undisturbing in 2000 miles of sailing the Carribbean. The ketch ran right up to 9.3 in a particular flat water squall between Yucatan and Cuba, and it was as smooth as a babies behind.

My most necessary improvement will be to immediately get a max prop before I surf the darn shaft out of the vessel entirely.

I got the Ketch because I though it represented a CRUISING boat, I know that sloops are all better for performance in every way except when stuff goes to heck and you wake up with a requirement to reduce sail in a howling wind, and you have to run up forward upon the deck and do stuff.
I run a sailing club, and we wanted a bigger boat to train people for Cruising. I thought that multiple masts would help a lot in teaching people to review the effects of one sail trim upon the other(s)

We had a couple of surprizes on the recent open ocean voyage, and the ketch was easier to reduce sail on because the main mast was closer to the central cockpit, which is yet another consideration.

I came from an Alden schooner, but before that a C&C 1 tonner sloop, so I have tried a few things.

I think that if you know what you are doing, and you are not racing into the wind, or straight downwind, the hull makes more difference than the rig, given the same amount of sail area.