Can I shorten my boom?

[Ted]

I bet naval architechs roll on the floor with laughter when somebody suggests making major modifications to the rig without having a clue about what it will do to the sailing characteristics of the boat.

But in this instance, Tartan and or Sparkman and Stephens were the ones making the changes to the sail plan not the OP. The OP was just asking if he could cut his boom to make it the length of the shorter boom that were delivered with the boats that were built later than his own. I don't see any rational reason why a designer/manufacturer would intentionally make a modification to a proven design that would detract from its sailing characteristics.

 

[agprice22]

Wouldn't a higher aspect ratio sails point higher? Removing several feet off the foot of the sail will change the aspect ratio. More luff and less drag in the draft. It should point higher.
A shorter foot will mean less weather helm. Lee helm will depend on whether he shortens or reefs his jib too to balance the rig.
It is a sailboat... if it were an airplane, I'd worry! However, failure in this situation will mean an accident at 8 mph...
Now if he was planing at 25 kts... then I might worry.
I think the main issue will be whether he balances the jib/genoa with the main.
Running a 150 genoa with a shortened main could be really frustrating. He would have lee helm when he would normally expect weather helm. Well behaved boats experience increasing weather helm as wind speed rises, so the boat naturally rounds up. On the other hand, I routinely sail further off the wind as it picks up. I can go off the wind or downwind in a gust when others are rounding up. It might ruin my course, but it keeps my speed up while reducing heeling.
He can always get another boom. In fact, I would arrange for an experimental rig, so I could keep my original rig. Get another boom and main to try if you can without ruining your original. You might not like the result. I think it would depend on my budget. If I could afford a boom and main with which to experiment, I'd go for it. You might even keep the other rig.

 

[lost soul]

Guys I have had a Tartan 34 for 20 years and have heard a few things about the history. The boat was designed in 1967 by S&S, that we know. I understand that it was designed to the CCA rule, as a performance ocean racer/cruiser. The original boom was about 14 feet in the design.

Then the IOR rule came into effect. Tartan shortened the boom to 12 feet and then to 10.5 feet. Scuttlebutt says that the boom was shortened to take advantage of the IOR rule. Scuttlebutt also says that the T34 had bad weather helm and the change of boom helped that. I am sure that the shorter boom was made by Tartan and not by owners. I have been told that sailors used very large head sails as they were "ok" with the IOR rule. Also they helped make up for that missing main on some points of sail. I am told that this was common for CCA boats to be competitive racing.

My 1974 Tartan 34 has a 10.5 feet boom. As far as I can tell, it was delivered this way. The boat has some weather helm and never has lee helm. I would think that if t he boom was longer the weather helm would be much greater. I have wondered why the boom was shortened. 10.5 feet boom with a P of 35 is not much sail, but it seems to sail well. I am no racer, except when another sailboat is near. I am just a cruiser who sails with his wife.

I do enjoy discussion of design and performance and appreciate this discussion. I would think that the "new high aspect rig" would be better going up wind. Of course performance would suffer off the wind.

My boom at 10.5 feet does not interfere with a Bimini. The wheel is mounted forward in the cockpit and the boom end is forward of this. It seems so short at times. I have a bridge deck traveler that the PO had installed.

I dont claim to be any authority, but just a guy who loves his boat.
Happy holidays....

 

[Stu Jackson]

Running a 150 genoa with a shortened main could be really frustrating. He would have lee helm when he would normally expect weather helm.

Not necessarily.

I've run our boat on just a working jib (110) or even a smaller 85% jib with NO main up and never had any issues.

Of course, that was back in San Francisco, where the wind was, well, there.

In light air, perhaps you could be right.

 

[Stu Jackson]

I am sure that the shorter boom was made by Tartan and not by owners.

Wouldn't one have to ask if the foot of the sail had been modified, too?

 

[shemandr]

I've wondered for years whether the higher aspect ratio of a main with a shortened foot would make up for the loss in sail area. At what point does the efficiency of the high aspect ratio sail overtake a reduction of sail area?
When I had my Mark 25, which was a souped up C&C, 25, I had a 40' mast, fractional rig and a 110 jib. The main was the engine. But, to give the main the roach which would have made the sail "High aspect" you would run into the classic problem - the backstay. So for decades, or maybe a century, the solution was running backstays. Unfortunately a mistake with the running backstays in a tack could lead to a drastic reduction in the boat's air draft. So I wondered if making the foot more short and the roach more full, but still avoiding the backstay, would provide a high aspect ration sail that would be more efficient and make up up the reduction of sail area.
Roll forward to last fall's Off Soundings regatta and a boat named Bagatelle. (http://www.ericwsponberg.com/boat-designs/bagatelle/) It is a custom cold molded build with the sail plan I wondered about. Non-overlapping jib, high aspect ratio main with a foot short enough to have a big round roach which doesn't catch on the backstay. We passed it easily last year in a J109, with a spinnaker, but it was light air downwind, and it wasn't flying the asym it is rated with. Soooo, I still don't know. The boat's results in races is mixed.
I understand the OP was not about performance but I'd like to see input from others on this question.

 

[CloudDiver]

I'm going to answer the OP's original question first without diving off the deep end about sail modifications and the effects of such on the sail plan... (but more on that later).
Can you shorten the boom? Yes, its pretty easy but plan ahead. Lopping off 3.5 feet from the outboard end could be a bad idea. You have to take into consideration the complete hardware setup on your boom, particularly if you have an internal outhaul. This is also a great chance to remove ALL hardware from the boom to inspect for bit metal corrosion and then re-bed all the hardware and/or use tef-gel on stainless bolt/screw threads. You might even consider painting the boom where age and current condition will be the determining factors. Anyway, when you decide how the hardware will be re-organnized on the shorter boom you can decide if you will be shortening from the outboard end or inboard end. The inboard end is more challenging because you will have to re-widen the sail track slot so the sail slides or bolt rope on the foot will feed back in.... you get the idea. The actual cut on the aluminum mast is simple, just be super careful to do a square cut. Use blue tape to protect the area of the cut and measure 6 times... a miter box and a hacksaw is the best low tech approach, I use a miter saw that has a blade specifically for non-ferrous metal.

Anyway... I don't mean to patronize, I get the feeling you are completely aware of how to make a correct cut on a boom but you were more concerned about the effects on the mainsail. Roger... My two cents are very simple there (because I'm no sailmaking expert). Lots of people are offering opinions about how the reduced sail area will effect the sail plan, and I'm not trying to second guess anyone's posts.... BUT, your situation is much different than someone just trying to do an 'unauthorized' mod. You have the precedent of the factory (and or original designer) making this modification to the sail plan. There really should be no question as to it being 'ok' for you to do the same thing was done all new boats following yours. I would just find a skilled sail loft to re-cut the main for the shortened foot and talk through the modification with them first. Touch base with other Tartan owners too, you might find some words of wisdom there.

This is kind of out there, maybe not something to consider but I think this is the kind of question to be asked; If your goal is to shorten the boom to provide head clearance while standing at the helm, would the 12 ft boom accomplish this rather than go all the way to 10.5 ft? In any case, would raising the boom height on the mast to provide head clearance while standing in any position in the cockpit be beneficial? Can the sail be cut for the 12 ft boom but with a shorter luff to raise it and still have the correct sq footage for the sail plan?

 

[rardiH36]

I have only done a 60 second "skim" of the responses so far. So apologize if someone also has picked up and responded as my following thought:

By the OP's second post (that would be #3 in the thread) is seems that primary reasoning for shortening the boom is so the boom can't clock him on the head. So I would guess the boom level is quite low.

Yes, shortening the boom would protect the helmsman (assuming his position is always at the helm and sometimes not more forward say if he has engaged the auto pilot and is standing looking around at things while sipping a cup of coffee). But also pity the poor passenger standing in the cockpit several feet forward. A shorter boom, but still a low hanging one, would still smack them in the head.

Another solution is to bring the mainsail to a loft and ask for the clew to be raised say a couple of feet. Or looking slightly differently, the leach length be shortened by a couple of feet. This mod will raise the boom level. For very little expense. And unless racing, because the lost sail area is right down low, the change in performance is likely to be unnoticeable.

I know that when my 1980 Hunter 36 was built, the "style" back then was for the mainsail often to be cut so the boom even drooped below horizontal. When I bought the boat in 2006, on board was still the OEM main sail. It allowed the boom to droop to my temple level. When an accidental jibe barely missed the head height of a 5'2" passenger who was standing on the cockpit floor, I quickly opted for a higher clewed main sail replacement. Problem solved. These days, for recreational cruisers at least, a higher of boom level at the gooseneck, and the cut of the mainsail leach length, will allow that the boom droop only to a level that is safely above head height.

 

[SOCAL C50]

I have only done a 60 second "skim" of the responses so far. So apologize if someone also has picked up and responded as my following thought:

By the OP's second post (that would be #3 in the thread) is seems that primary reasoning for shortening the boom is so the boom can't clock him on the head. So I would guess the boom level is quite low.

Yes, shortening the boom would protect the helmsman (assuming his position is always at the helm and sometimes not more forward say if he has engaged the auto pilot and is standing looking around at things while sipping a cup of coffee). But also pity the poor passenger standing in the cockpit several feet forward. A shorter boom, but still a low hanging one, would still smack them in the head.

Another solution is to bring the mainsail to a loft and ask for the clew to be raised say a couple of feet. Or looking slightly differently, the leach length be shortened by a couple of feet. This mod will raise the boom level. For very little expense. And unless racing, because the lost sail area is right down low, the change in performance is likely to be unnoticeable.

I know that when my 1980 Hunter 36 was built, the "style" back then was for the mainsail often to be cut so the boom even drooped below horizontal. When I bought the boat in 2006, on board was still the OEM main sail. It allowed the boom to droop to my temple level. When an accidental jibe barely missed the head height of a 5'2" passenger who was standing on the cockpit floor, I quickly opted for a higher clewed main sail replacement. Problem solved. These days, for recreational cruisers at least, a higher of boom level at the gooseneck, and the cut of the mainsail leach length, will allow that the boom droop only to a level that is safely above head height.

My thoughts exactly... If you chop the end of the boon off a recut mainsail will end up costing as much as a new one, generally the loft wont do that type of mod. BUT they will tuck the foot up by shortening the shelf some (kinda like a tummy tuck) and as a cruiser I'd have the loft recut the foot to become a loose footed main. Check with the loft before modding your boat, a good loft might even take a ride with you to see what you need and suggest mods as needed by a professional.