Raising and shortening mizzen boom

[DarwinHolmstrom]

I'm considering raising and shortening the mizzen boom on my ketch. This will enable me to install a Bimini, a Hydrovane, and a stern arch with dinghy davits and afford a place to mount solar panels and a wind generator. This shouldn't decrease the power of the sail too much because most of the power is generated in the upper portion of the sail. Has anyone else tried this?

[kenbo]

I did something similar to what you have proposed but I used a taller mast that I found used and kept the same sail. I incurred rigging expense but little sail cost, I had to change the sail slides.

[DarwinHolmstrom]

Originally Posted by kenbo

I did something similar to what you have proposed but I used a taller mast that I found used and kept the same sail. I incurred rigging expense but little sail cost, I had to change the sail slides.

I can get my existing mizzensail altered to fit, which won't cost much. Did you notice much of a change when sailing?

[kenbo]

I did not under normal conditions, but I did get knocked down once in the Gulf of St. Lawrence under reefed mizzen and #3 jib. Did not have a wind speed instrument but it was sporty. The boat was an Allied Seawind II and I always wondered if raising the CE a bit was the blame but the boat was so challenged on SA/Disp that I really didn't want to do what you're proposing.

Never sailed on a Shannon but have heard that they tend to be initially tender. If that's so I wouldn't use my approach.

[DarwinHolmstrom]

Originally Posted by kenbo

I did not under normal conditions, but I did get knocked down once in the Gulf of St. Lawrence under reefed mizzen and #3 jib. Did not have a wind speed instrument but it was sporty. The boat was an Allied Seawind II and I always wondered if raising the CE a bit was the blame but the boat was so challenged on SA/Disp that I really didn't want to do what you're proposing.

Never sailed on a Shannon but have heard that they tend to be initially tender. If that's so I wouldn't use my approach.

Yikes! My Shannon weighs 20,000 pound and it's a handful when it's on the rails. Do you think you would have been knocked down if you were running the mizzen and the staysail?

[kenbo]

The Seawind II was 15,000 lbs unladen on a 25.5 LWL. We were fully laden I'm assuming around 18,000 lbs. She was and remains the most confidence inspiring yacht I've sailed on. Did not have a staysail, the hank on #3 could have had a reef put in but we had not done that and put a single reef in the mizzen and struck the main. The boat was balanced but she became over powered by the strength of the gust.

I mentioned before that it was very sporty and my crew and I never really agreed on the wind gust strength but the estimates were north of 50kts.

[DarwinHolmstrom]

Originally Posted by kenbo

I mentioned before that it was very sporty and my crew and I never really agreed on the wind gust strength but the estimates were north of 50kts.

Yikes again! I slept--or rather tried to sleep, without much luck--on a boat tied up at a slip in 50kt winds one night and that was an extremely rough night. I can't even imagine being out on the water in those conditions. If I had any diesel left, I think I'd be motoring if I was caught in winds like that.

[kenbo]

The question you have is, I believe, what will be the effect of moving my CE up and forward by your suggested change to the sail plan. My change moved the CE up only.

What is your helm balance like now? You mentioned that when the rails are in the water she's a handfull. Is that weather helm mostly? If so, then moving the CE forward may help with that.

Consult with a knowledgeable sailmaker.

[DarwinHolmstrom]

Yes, that was exactly my question. Just shortening the sail will take a small amount of pressure off of the lower portion of the sail, which mathematically probably does increase pressure on the smaller upper portion of the sail, but it won't be as dramatic as moving the entire sail and the weight of the mast up higher. The tech I consulted didn't think it would have a noticeable effect on the center of gravity or much of a decrease in speed, but I was worried about something very much like what happened to you. This has been helpful. Thank you.

[kenbo]

The CE is not the center of gravity, it is the combined center of effort of the sail plan. Its relationship to the center of lateral resistance (CLR) determines the balance of the boat/helm.

[Cheechako]

I think you will be fine. A taller mizzen will move the CE forward just a tiny bit in the mizzen if anything. The total CE will then move even less. Heck many people never use their Mizzens at all in normal weather and sail just fine.
You could consider just shortening the boom and forget more height. How do you use your mizzen? Mostly just in heavy weather?
How does your boat sail with no mizzen up? Can you eliminate it? Rake the main mast aft a bit? New longer boom and mainsail?

[DarwinHolmstrom]

Originally Posted by kenbo

The CE is not the center of gravity, it is the combined center of effort of the sail plan. Its relationship to the center of lateral resistance (CLR) determines the balance of the boat/helm.

Thank you! I was translating this into motorcycle physics! When you build a bike for road racing, you keep the weight as centralized as possible because that's how you make the bike flip from side to side smoothly and efficiently. That's why unsprung weight is such an important factor on a race bike. A lot of the physics involved in road racing motorcycles translate to sailing, to a degree. This is a good example of why they don't translate directly.

[DarwinHolmstrom]

Originally Posted by Cheechako

I think you will be fine. A taller mizzen will move the CE forward just a tiny bit in the mizzen if anything. The total CE will then move even less. Heck many people never use their Mizzens at all in normal weather and sail just fine.
You could consider just shortening the boom and forget more height. How do you use your mizzen? Mostly just in heavy weather?
How does your boat sail with no mizzen up? Can you eliminate it? Rake the main mast aft a bit? New longer boom and mainsail?

I only had my boat about a month before I had to take her out of the water for the winter but I tried as many combinations as I could. Mostly I used the genoa, and the main, and the mizzen, but also the staysail and the main and the mizzen and genoa. We got in a bit of trouble with that last one when we got caught in two colliding fronts and had wind coming from two directions. That was when we had her on her rails. I think we might have been better off with the mizzen and the staysail, both reefed.

[somanyboats]

we raised the mizzen boom on our Cheoy Lee offshore 41, did not shorten it. Had the sail recut, all for the same reasons you mentioned.
It worked out great. We did not notice a difference when sailing

[DarwinHolmstrom]

Originally Posted by somanyboats

we raised the mizzen boom on our Cheoy Lee offshore 41, did not shorten it. Had the sail recut, all for the same reasons you mentioned.
It worked out great. We did not notice a difference when sailing

Thank you. It seems like this is the best solution for living aboard a ketch.