hypothetical Re-Rig

[Ben M-P]

I am trying to learn how to redesign a rig from Marconi to Gaff.

Here is a design I did:
The boat it a Hardin Sea Wolf 40
The original sail-plan was about 780sq.ft.
The modified plan is 938 sq.ft (should have paid more attention to this)

Is this anywhere close to what a re-rig like this should be?

Should the main and head sails be smaller?

Also, what would be required to actually make the modification on a real boat?

[PAR]

Generally, this sort of thing is best left to professionals, for several reasons. The most obvious is the now considerably farther aft CE location. Assuming the CE lead previously was in the 12% range (typical for a ketch) you've now got it in the neighborhood of 5% - 7% which isn't enough, in spite of the "slack" this boat's full length keel offers in this regard.

Almost always, the mast(s) have to move as well as chain plates, which typically is much more then an owner is willing to invest in. It's not a lot of money to redraw the rig properly.

To get the proportions looking right and to move the CE back where it belongs, the main should move forward. I know the berths get in the way if you go too far, but 18" might be enough. This will reduce the fore triangle a bit and give the mizzen some breathing room too. If I drew it, the gaffs would have considerably more "peak" so they can be hardened. I would also shorten the main mast, toss in some runners and maybe a main topsail, not to mention keep the area within a reasonable range.

Other then looks, is there a reason for this treatment?

[Mark Johnson]

It will be an expensive step backwards performance wise, and likely in ease of handling as well, but if you really like the look... "Wild assed guess" would be $20,000 to $30,000 for starters... minimum. (IF it is an after the fact retrofit).

What you've drawn looks like you are in the ball park. I suggest that you send your drawings to a trusted navel architect, to double check what you have, and for the final placement of things. If he doesn't have to spend too much time on it, it would be surprisingly inexpensive.

I made changes to my rig based on conversations on the phone with the designer. Then "I" drew what he proposed, and sent it off to be double checked, as I suggest above.

This is a case where 2% more money (spent on the entire mod), can triple the likelihood of getting it just right, rather than OK, but out of balance. There may be other considerations that you don't yet see as well...

It is money VERY well spent! Designers draw a boat the way that they do for a reason. If you plan to make such major design changes, it is best to know why it was drawn that way in the first place. IMO...

Mark

[Ben M-P]

Thnaks for the input.

PAR,
I'm not sure I understand about changing the lead, I was under the impression that the lead had to do with the CE in relation to the CLR, both sail plans have almost the same CE. Does a gaff rig need a different lead, or is there more to it?
I have heard that the gaff rig offers more flexibility (topsails, more adjustments to the sails, etc.) and also is a lower stress rig.
I also like the "salty" look.

I should say that I don't own a boat at the moment and am trying to understand the basics of NA as it relates to re-designing a sail plan not actually doing it at the moment.

[Ben M-P]

One question, when adding light wind sails (topsails, gollywobblers, drifters, etc.) to a sail plan the the CE must be kept in the same location fore and aft (is that right) is it also important to keep it in the same position vertically?

[PAR]

Ben did you use the headsail areas and centers individually or did you use the fore triangle area and center to calulate your CE? Judging by it's (the gaff version) location, I assumed you used your headsails and their respective centers.

[Ben M-P]

PAR,
I used the separate centers.
I was trying to see how little I could change the rig(same masts, jib, re-cut mizzen) and still change it over.
I was looking at the sail plan and as my brother said,"that is about the ugliest gaff rig I have ever seen."

Thanks for all the help and suggestions.

[PAR]

I wasn't going to offend your drawing, but your brother is onto something.

I knew you used the separate sail areas and centers, but wanted to hear it from you as confirmation. Typically we use 100% of the fore triangle for the area and center, not the separate sails, particularly with multiple headsails.

There are other obvious issues as well, so it's not necessary to dissect the whole thing, but to suggest a professional draw up the rig. Again, as has been previously noted, it's not a difficult proposision for a designer, so modest in price. The real costs will be the new rig. You'll likely be able to keep the main mast, though it'll need to be cut down and moved. The chain plates will also move, so internal supports in the hull will be necessary. Additional chain plates and local reinforcement for the mizzen, the mizzen mast and of course a new set of sails (no, the old ones can't be cut into a gaff rig).

Performance will not suffer as much as previously mentioned, simply because you're starting with a ketch anyway. The look of the yacht will change dramatically, as will the way she's sailed (string pulling stuff), but an interesting conversion.

[Ben M-P]

Thanks for all your help I really appreciate it.
Is there a good book on the subject or a way to learn about how to do the design work.
I hate to keep asking questions that require long complicated answers.

Or is Westlawn the best place to start.
Thanks

[PAR]

There are several books that could be helpful, though it's few different disciplines you'll need to have a handle on. Westlawn is an option and their short course may be enough for you, though a hell of a lot more costly then just hiring the task out. "The Design of Sailing Yachts" by Gutelle, "Skene's Elements of Yacht Design" by Kinney, "Principles of Yacht Design" by Larsson are the usual suggestions.

[smithy]

Ahoy, Ben - good to see you here too.

- Chris

[Ben M-P]

Thanks PAR,
I'm trying to get enough knowledge about this sort of thing so that I will be able to figure out what I want and work out a basic design that I can take to a designer for improvement.

Hi Chris (Tidewater forge?)

[smithy]

Yup. Working on a Macgregor 22' for my scouts, lotta great info here.

Good luck with your project.