Mast calculations -need assistance please.

[Manateeman]

Greetings. The vessel is a 60’ aluminum twin keel ketch which never has been rigged. I think this is the link . Ted Brewer Yacht Designs https://www.tedbrewer.com/sail_aluminum/shenanigan.htm
We wish to reduce the air draft to 64’
We would deeply appreciate expertise is evaluating a Pacific Spar we have purchased and suggestions to reduce sail area including variations of wishbone gaffs. We do not wish to open a Pandora’s box on wishbone rigs but first things first...reducing air draft. Lastly, we are old boatbuilders and have no need for performance offshore.
Serious responses please.
Here are the particulars for the vessel.
LOA 60’ LWL 56’ Beam 17’ Twin keel draft 6’ Displacement 65,000 Ballast 21,00
Prism .545 , one degree heel, 6,100 Righting moment 30 degree 61,000
VCG=LWL, Center Buoyancy -3.3
The main mast as drawn 77’ with moms of 153 x 65. Keel stepped, thus the keel, mast partners and chainplates can support high loads.
We acquired a Pacific Spars mast with the following dimensions:
Length 63.5 feet. Oval. 10 x 7” with moms of 58 x 30.9
Two sets of spreaders which match existing chain plate position, and set for staysail and Genoa. This was a deck stepped spar on an unknown vessel.
We intend to keel step it.
Obviously, both sets of spreaders will be closer to the deck. The original spreader positions divided the spar in thirds. Keel stepping the spar lowers the entire spar by 7 feet. Thus the first issue was the risk of moving the spreaders up the spar.
I personally dislike more hole for such a small gain.
We will construct a 1 foot high compression post on the keel. The Pacific Spar heel wil still be one foot under LWL.
We TIG weld thus moving and fabricating the boom is not an issue.
Obviously...this is a “light” spar given the boat.
Reducing the total sail area by what proportion becomes the critical question.
Keeping a ketch rig as a given still open discussion as to the particulars.
I would appreciate the collective knowledge here on the following:
Reasonable sail area for the Pacific Spar detailed above.
Main sail and boom...conventional calculations.
Options for reducing mast pressure with wishbone rigs including wishbones which can be easily lowered. I realize this opens the Pandora’s box but this might be an interesting discussion on large sailboats for old people.
I thank in advance, the collective expertise and close with kindest regards to all.
Mark the manatee

[GordMay]

Greetings and welcome aboard the CF, Mark.

[billknny]

If I was you I'd pay Ted Brewer a consulting fee for his opinion. They likely have access to more data and calculations on this design than anybody else.

I assume they could give you better guidance than a bunch of random strangers for the cost of an hour or two of their time, and his consulting rates seem really reasonable.

[jmorrison146]

billknny is on the money!

[GordMay]

If you would like to consult with Ted Brewer personally, a fee of $350 US will enable you to contact him as many times as necessary, within reason of course, to ask questions about hulls, rigs, construction, Brewer designs, or any other boats you are considering. E-mail is the best way to reach him. To talk to him on the phone, it is best to send an e-mail, and make an appointment (Ted no longer keeps regular office hours) for a phone call.
Brewer Yacht Design
1825 Evergreen Drive,
Agassiz, BC V0M 1A3 CANADA
Tel: 604-796-3732
Fax: 604-796-3738
E-mail: brewer@island.net.

[Manateeman]

My wife and I purchased the hull and deck from the couple who paid Mr. Brewer for this custom design. We have all the original drawings. One might assume asking a few questions relative to the design, would not be unreasonable. I’ve never spoken to Mr Brewer and I believe we asked only one question shortly after acquiring the boat and drawings.
I wrote Mr Brewer an email on 9-29. To date, no reply.
We recognize he is retired and that legally, he might not be obligated to reply or he may be indisposed. I knew the original owner and we discussed the design of this boat at length. I felt Mr. Brewer did an outstanding design.
I have had detailed discussions with two other designers and two experts in spars and rigging. As I have worked for a number of yacht builders over the years... such professional courtesy toward older fellow builders, is common. I have asked the collective knowledge of this forum in the hope to gain new perspectives and thinking on the subject of reducing air draft.
Contacting the designer is a sound idea and I appreciate the reply.
Kind regards, Manatee

[Bill O]

Rigged a double spreader mast for an older 40' sloop from scratch after consulting a naval architect at Offshore Spar. He pointed me to a reference book (Skene's Elements of Yacht Design. by Norman L. Skene) which provided many of the calculations needed to complete the project.
Before building the mast, I had the NA go over my calculations and they were fine. His only comment was on the wire size (went next size up). My reply was that I wasn't building a race boat (they built many America's Cup masts) and wanted the extra safety margin offshore. He was ok with that answer and went off to assemble the mast.
Biggest take away from the my mast project was there was a wide % spread where you could place the spreaders and still have good panel tension. The calculations were not that difficult (if you're good w/math), but would second a review of your calculations by a profession NA that specialized in rigs.
Obviously you found out retrofitting a spar that was set up for a different boat isn't necessarily the easiest in the long run. This is especially true if you are trying to modify a deck mount to fit a keel stepped since all the winches, etc will be in the wrong spot make the mast base Swiss cheese. Rather than lower your mast and having to move spreaders etc., why not try to sleeve a 7' or more to the base? It will be stronger at the sleeve than the rest of the mast and less playing around w/the mast step, winches and other hardware placement.

Had to chuckle on the Ted Hood's whimsical naming of model of your boat "Shenanigan". Hope he didn't do much of that when he designed the boat!

Bottom line, you should seek out a professional NA that can help you make certain your rig design is sound rather than free advise (you get what you pay for).


Good luck on the project.
Bill O.

[Nicholson58]

I noticed in your link that the planned rig is very similar to ours on a 1984 Camper & Nicholson 58 ketch. Yours also shows a cutter. We find Caribbean sailing with powered in mast furling we use the cutter most of the time. Our rig ie 80 air draft. The only time this has ever been an issue was when we wanted to use the ICW. I can understand if you plan to need access to the ICW that you would shorten the rig, however, I thought the magic number was 63 feet.

I agree with the others that asking the designer or other qualified rigger or marine specialists is your best option. Asking CF folks to come up with a design would be like starting an anchor discussion.

I like keeping the two mast approach. It’s likely to look more like a schooner. The mizzen gives you the option of a mizzen staysail. It’s the easy, poor mans spinnaker on our boat. I can rig and hoist it easily and quickly. In air up to around 10 it adds a lot of off wind boat speed.

If you can, keep the slot area between the fore stay and cutter open enough that you can run both sails on occasion. Is it possible you might get to a single spreader?

[Cheechako]

I totally agree with contacting Ted or another naval architect. I did this once with a noted architect on the rig for a boat I built. It was super interesting and worth the money just for that to me. He filled me in on some of his past popular designs and was forthcoming on the pro's and con's of how they came out. Also providing insight as to why he thought those things occurred etc. We sat and had a glass of Jameson when done too!

[Manateeman]

Thanks to all who have replied. I had Skenes book on my shelf for decades. My personal favorite is Principles of Yacht Design by Lars Larson, Eliasson and Orych. Thorough discussion on rig construction.
The objective of my post was to listen to members thoughts and experiences with regard to options in reducing air draft to accommodate the desires of older cruisers or those who wish to do the ICW or...wish to have a large boat with a small sail area. The objective is to open a discussion of alternatives for older sailors who are simply not comfortable with a big rig.
I consider myself a very skilled boatbuilder but the older I get, the more I realize neither myself, nor any professional naval engineer, can both keep up with technology and at the same time, learn from the vast experiences of the past.
Two stories might illustrate my thinking. Please bear with me.
I grew up on Buzzards Bay. My Grandfather’s boat was a Roaring Bessie. It had two completely different rigs. A summer rig with tall spars and long bow spirit and a winter rig with greatly reduced sail area, far shorter spars, a ton of beach rocks and midship washboards to ward off errant waves. There is a model in the Providence Library. She was based on working fishboats from No Mans Land.
My wife and I are simply not interested in 70 plus feet of spar.
Advice to see a “architect “. Reminds me of the time I visited the studio of a well known designer. I simply wished to extend the bowsprit on his design. I told him that Ben Hall of Hall Spars had graciously checked all calculations. He had the reaction of a petulant child. I withdrew with apologies.
My point is simple. Boatbuilding is an imprecise science which historically has benefited from the open and civilized sharing of thoughts and ideas.
Looking forward to the discussion.
Mark the manatee.

[Cheechako]

Originally Posted by Manateeman

Thanks to all who have replied. I had Skenes book on my shelf for decades. My personal favorite is Principles of Yacht Design by Lars Larson, Eliasson and Orych. Thorough discussion on rig construction.
The objective of my post was to listen to members thoughts and experiences with regard to options in reducing air draft to accommodate the desires of older cruisers or those who wish to do the ICW or...wish to have a large boat with a small sail area. The objective is to open a discussion of alternatives for older sailors who are simply not comfortable with a big rig.
I consider myself a very skilled boatbuilder but the older I get, the more I realize neither myself, nor any professional naval engineer, can both keep up with technology and at the same time, learn from the vast experiences of the past.
Two stories might illustrate my thinking. Please bear with me.
I grew up on Buzzards Bay. My Grandfather’s boat was a Roaring Bessie. It had two completely different rigs. A summer rig with tall spars and long bow spirit and a winter rig with greatly reduced sail area, far shorter spars, a ton of beach rocks and midship washboards to ward off errant waves. There is a model in the Providence Library. She was based on working fishboats from No Mans Land.
My wife and I are simply not interested in 70 plus feet of spar.
Advice to see a “architect “. Reminds me of the time I visited the studio of a well known designer. I simply wished to extend the bowsprit on his design. I told him that Ben Hall of Hall Spars had graciously checked all calculations. He had the reaction of a petulant child. I withdrew with apologies.
My point is simple. Boatbuilding is an imprecise science which historically has benefited from the open and civilized sharing of thoughts and ideas.
Looking forward to the discussion.
Mark the manatee.

Well now that more is known about you and your past then maybe you don't need an architect's input. Everything like that is a learning experience though.
But your parameters are set somewhat which makes it easier: Your height above water is the driving dimension. I would simply work from there and get the CE of the Main as it is, then start looking at foot length and see how close you can get to the original CE. I'm personally a fan of lee helm, or nearly lee helm, although many aren't . Far more pleasant sailing.
I totally agree with "Boatbuilding is an imprecise science" and have argued a bit in the past with some here when discussing bowsprit additions etc. My point in those arguments is: any time you change, reef or furl sails you change the theoretical helm and CE of the rig. So being too precise in a theoretical sail area on paper isn't too important.
It's important to keep a column straight to avoid "column failure". So two sets of spreaders is better than one, especially once you get to a certain length. I think you can look at what boat lengths/mast lengths designers normally go to two sets of spreaders and just use that rule.

[TrentePieds]

Quote: "I wrote Mr Brewer an email on 9-29. To date, no reply."

I will be at a meeting tonight where Mrs. Brewer may also be in attendance. I have a distinct impression that Ted is not much interested in either design or consulting work any more, so I am not surprised that you've had no response from him.

If she is at the meeting I will ask Mrs. Brewer if he is entertaining these sorts of queries at all any more, and I will post her response in this thread.

The question you pose is really more than a 350-buck question, and not one that anyone who takes liability seriously should presume to answer on a chat board.

If you have the necessary background in engineering I suggest you do the calculations yourself. If you have Skene's Elements (Francis Kinney) as well as Larson, Eliasson and Orych under your belt, you can do the stability calculations yourself on the basis of what you stated in post #1 above. So that leaves only the calculations required to dimension the actual spar and its staying.

I will let you know what Mrs. Brewer has to say. Should Ted prefer not to engage, then I suggest you find someone else - or study hard enuff and long enuff to deal with this particular problem yourself. It is, after all, only a tiny subset of engineering.

TrentePieds

[Michael Pope]

Leave Mr Brewer enjoy his retirement us oldeys deserve it. If you know someone with a MIG welder Get him to weld up the holes in the mast tube I used to work at one time for Pacific Spar) Whack the power to it and then machine in smooth and shiny . If you are clever put a dam on the inside of the hole so the weld does not interfer with the internal halyards if you use them. Let each one cool before you do the next. and do notpussy foot arround with a small wire feed . The time welding is what gets it too hot and destroys the T 6 temper in the alloy.
Then draw a new mainsail with a BIG ROACH and Full length Battens except for the bottom one. You will be amazed at the performance improvement. It does not hurt to extend the Backstay tang back a few inches as well. I did that on one 38 ft IOR type rig and the cruisers accused me of having an electric Aux Motor because I could sail around and go fishing with just the main I had shortened the Boom as well. Make slides for the inboard ends of the battens as well easier on the Luff rope or track Happy boating
I think an odd looking spreader setup really cheapens a boat. Good luck Mike Pope

[billknny]

Originally Posted by Manateeman

Looking forward to the discussion.
Mark the manatee.

Mark,

I am not at all sure what your question actually is... You have decided what to do, just do it.

You'll have a functional motor sailor with a SA/D ratio somewhere down near 10-12 or so. You'll not be sailing in anything less than 15 knots of apparent wind, but I suspect you are sophisticated enough you already know that.

The boat has a big engine and huge fuel capacity. It will get you where you want to go. It's just like the original design just sailing with a constant 2nd reef. You'll have a much lower moment of inertia, so the boat will be a bit rolly, but I don't know it that will be uncomfortable or not.

It's not the boat I would chose, but no boat is perfect for everybody, and no boat is perfect for anybody. You are making some HUGE compromises on sailing performance for other benefits. Only you can now if that is right for you.

If you want someone here to argue with that, they will. If you want someone here to tell you your design mods are perfect and the way the boat should have been in the first place, somebody will do that too...

[Manateeman]

Thank you all. I had hoped I would have learned a bit more about everyone’s thoughts on wishbone rigs and that perhaps there were solutions out there to achieving more sail power without going vertical. There is a lot of nice space between the spars in a ketch and I thought cruisers might have seen interesting ways to fill it. The solution might simply be two rigs for the mainmast. One for the ICW, one for offshore. A knowledgeable rig designer told me to call all the carbon fiber mast builders as they would have a list of aluminum spars they had replaced with carbon. This proved to be true and I purchased an entire rig which sits in Maine and is for sale. A long silly story...just not the right rig for me.
He also told me to contact 12 meter folks as I might find a perfect spar for a good price. I looked at a Rondel which was truly beautiful and sold before I could make an offer. I think the Pacific Spar is very well made. I have a TIG inverter onboard. I love TIG welding aluminum. One of the joys of an aluminum boat.
I’ve built in wood, glass and epoxy and worked for a half dozen builders. I wish I had learned to TIG before I learned to line up ducks on the floor.
I know that Bruce King had a carbon fiber wishbone ketch but I’ve lost the photos. I would also appreciate references to alternative sail plans for ketch rigs.
Again, sincere thanks to all who reply. Mark the manatee.