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-   -   Raising the boom (http://www.sailnet.com/forums/gear-maintenance/14661-raising-boom.html)

claudialuso 04-13-2006 10:25 PM

Raising the boom
 
Hello!
We are refitting our boat.We have a scunna with double equal size masts. The boom is standing 5' from the deck. I would like to know if I raise the boom to clear 6' from the deck will that change deminish the boat performance.I would greatly appreciate your comments.
Thank you.
Luso

Faster 04-13-2006 10:42 PM

While I'm not familiar with your particular boat, a couple of issues will arise from raising the boom as you propose.
First, the sail(s) will need to be modified due to the shorter hoist caused by moving the boom up the mast. This will of course cost you sail area (power) in the end. (and cost some $$ - not much though)
Second, this will overall raise the center of effort of your sailpan, possibly making the boat somewhat more tender.
You may also run out of length on your sheet as the total distance from boom to boat will increase as well.
Generally the designers knew what they were doing... overly high booms can look somewhat odd too.

Irwin32 04-14-2006 08:42 AM

I would have a few local experts take a look at your boat - a surveyor, or even a naval architecth. Lots of people make changes to thier boats that effect the performance - adding ballast removing it would be an example.

I wonder how much effect 12" off your mainsail at the the masthead is going to have. Yes,the CG will raise a little bit, but if your boat is already stiff....

One good way to see what it will do to the asthetics is to find a line drawing of your boat, scan it, and then make the changes there to get an idea what it will look like.

Faster may well be right, but you really do need to have someone actually look at your boat that has experience in this type of thing.

Sailormon6 04-14-2006 09:18 AM

You don't say why you want to raise the boom, but, reading between the lines, I assume you just want more clearance for people and perhaps a bimini. The easiest way to raise a boom is to have your sailmaker install a cringle for a flattening reef about a foot above the sail's clew. Ease the mainsheet, and use your reefing gear to pull the outboard end of the boom up to that cringle. It doesn't sound like much, but it's surprising how much extra clearance it provides, and it doesn't sound like you need much clearance. It might be just enough for your purposes. Canting the outboard end of the boom up by a foot isn't very noticeable, visually, but if you try to increase the clearance by raising it 1.5 ft., it'll start to look odd.

Adding a flattening reef is not expensive, and using it like that doesn't cost you a terrible amount of sail area, and it doesn't ruin your sail shape. Obviously, the boat will perform better with it's factory configuration, but a flattening reef will accomplish your purpose, and, for general cruising, the boat's performance will be satisfactory. If you want to race or if you need all your sail area in light air, you can just shake out the little reef, and your sails will be back to factory configuration.

If you make any more "permanent" alterations in your sails or rigging, such as cutting down your sails, you'll undoubtedly hurt the value and marketability of your boat.

sailandoar 04-15-2006 08:40 AM

Balance of the sailplan ????
 
If sailing the boat is a small part of what you do with it then changing the sailplan won't matter much, but if the boats sailing ability is important to you then you will likely need to make other changes to maintain balance in the sailplan. Otherwise you might consider as was suggested in a previous post a sort of reef to temporarily raise the sail a bit as needed. You have not given any information of your vessel or rig and that makes commenting difficult.

Our schooner has gaff jaws on the booms and so they can be raised up as high as needed but many boats have goosenecks and of those some are on a slid and so can be adjusted up and down at least a bit. For us when we need the boom raised we take in the first reef and then use the throat and peak halyards to raise the whole sail assembly and so the boom as high as needed.

I think that the change in the vertical placement of the sails center of effort is not a great concern. More problematic is the change in the combined 'CE' of all sails. When headed down wind the reduction in sailarea in the aft most sail is not a big problem but when reaching (broad or close) the balance of the sail plan is changed in a way that may make the boat preform poorly. IF you have reef points then just tie in the first reef on the sail you are thinking about changing and try it. However, if the reef you have is much different from the change you are contemplating then maybe you should have a reef installed that duplicates the change you are contemplating and try it out. If it works for you then make all the other changes involved and 'life is good."

claudialuso 04-16-2006 11:55 AM

Raising the boom
 
Thank you all so much for your replies, it helps to see others' views.
A little about our boat:It is a 52' metal hull designed by Carof and built in Belgian. It has two 52' masts, a furling genoa and an inner jib. The booms are 14'5" long. The boat displacement is 30,000 tons.We were thinking that if we could raised the boom to 6' we could install a permanent top to the cockpit and it would also lessen the danger regarding boom moviments.We are not experienced sailors, just aspiring ones. We bought the boat five years ago and we are refiting it to fulfill our dreams of sailing around the world ,I'm sure you all know that dream well. So thanks again for your help. Luso & Claudia

Faster 04-18-2006 12:22 AM

Big difference raising a boom 12" on a 25' boat vs a 50+ footer... Can't imagine any great upset doing so on a boat that size!
That said, the suggestion to raise the clew with a "flattening reef" type set-up also makes sense.
Good Luck!!

sailandoar 04-18-2006 06:40 AM

Boom 6' off the deck?
 
How will you manage the sail when it come too, stowing, reefing, covering etc etc.

Unless your monetary investment in the boat is, triaval/disposable/'of no concern' you should consider consulting a naval architect. If you are not already members you might look into the Metal Boat Society. There are serveral NA's who advertise and participate regularly in the forums.


Be careful modifying the rig if the sailboat sails well now. If you had a sports car and wanted to carry piles of gear and you wrote into a forum and asked about cutting a hole in the roof to expand the cab so as to add storage I might suggest that you sell the sports car and buy a station wagon. Not that your idea is exactly like my wild example but it is a big deal to change the rig.

Don't mean to give offense and you have done the right thing asking questions but changes to the rig are potentialy 'life altering' and should done with a bit more research than just asking a bunch of strangers hanging around the marina what they think. It is not always easy to tell the difference between folks that .......... well you get the idea i'm sure.

Consider if there are other boats that meet your needs/requirements better than the one you have now and if you should switch boats.

RichH 04-18-2006 09:44 AM

Luso
New sailors rarely raise sails correctly and it may be that in not raising these sails fully the boom is not raising properly causing the boom to ride lower than the 'intended design'.
Assuming that you have sails made of dacron polyester on 52 ft. masts. would indicate that the luff of the sail would be in the range of about 46 ft.
Next time, try raising the sails in the following manner: Raise the sails, then apply an additional approximate 5 inches of 'stretch' with the halyard ... the boom end shoud raise approximately 5+ inches.

If the sail is made from dacron polyester and has a 'rope' in a sleeve at the luff, this rope has to be stretched by about 1" for every 12" of luff length. The rope in the sleeve at the luff is callled a 'boltrope' and when making the sail the sailmaker will purposely cut the rope shorter (1" for every 12" of luff length - call 'preload') so that the sail will be stable when fully wind loaded at its usual maximum wind range of 15-18 knots. If you dont stretch out this preload, the sail wont be fully raised and the boom end will be much lower than the design. Applying the correct halyard tension will raise the boom end .... and you may have the desired 'clearance' beneath the boom --- simply by raising the sail correctly.

If this is an old, well used sail it may be that the boltrope has simply shrunken (and become fatter) as every time you raise and then relax the luff this three strand rope becomes shorter. If so, you can take the sail to a sailmaker to 'ease' the boltrope; then, when raising the sail to the correct halyard tension the boom end will be much higher because the 'head' of the sail will be able to be raised higher on the mast !!!!! Raise the sail and with the winch 'crank' an additional 5-6 inches of halyard after the sail is 'up' .... I'll bet that the problem is that you are not applying sufficient halyard tension and this causes the boom to be much lower than the original design.


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