Cal 34 Mk III Rig dimensions

[thebastidge]

The Owner's Guide says the boom is 10'. The rig dimensions drawings I have found show the boom marked as 8-14.00 ft. (boom height above cabin top is marked as 3'11")

I have the original boom from my boat, and it is 10'. But I bought my boat without a mast, and the replacement rig I bought (originally a J35 rig) came with a matching 14' boom. I'm generically aware of the ratio between mast and boom, worries about too much weight outboard for the designed righting moment as well as concern about over-powering with attendant heeling and danger in a blow.

But I'm also wondering how much it matters if the original was designed with a range of boom lengths in mind. Cutting down the replacement boom and re-routing the internals, or changing out gooseneck and re-conditioning the original mast (no internal outhaul) to work with the replacement mast... seems very expensive. Even the longer boom won't interfere with the single backstay. The replacement mast comes with slightly-back swept dual spreaders and is a cutter rig. I'm planning to keep the fractional AND the masthead forestays, probably with a bowsprit for the jibstay, and possibly running the cutter stay to the original forestay or possibly to a new additional chainplate installed at the anchor locker bulkhead.

I imagine I could always run a main sail with a foot less than max boom length...

Thoughts?

I mean I already know that a cutter conversion is not the same as a cutter design. I'm interested in this because:

A: I already have the rig, with dual furlers, and
B: it gives more options for light winds, as well as lower power storm rig on the inner forestay.
C: I can get further out ahead for light air and moderate weather helm on a sprit, while lightening the loading on the sprit because it will be split between jibstay and inner forestay.
D: if a forestay were to be damaged, there's still another forestay to hold the rig up until repairs can be effected, so redundancy.

Additional philosophy- I know there is always the concern of racing against weather, but I am interested in cruising, not racing other people. I want a rig that can be single-handed, will be easy to sail with my wife as my only crew most of the time, that is safe and redundant.

[thebastidge]

Talking to someone on FB in the Cal Boats group who has a Mark I, and the rig was shorter by about 3'; I knew that. But his rig had a longer boom too; 14' and traveler located *behind* the tiller. That matches up with the rig diagram and gives me confidence my 14' replacement boom is do-able without affecting stability too much, since the Mark I and Mark III have the same hull, same ballast, and therefore something very close to the same righting moment. My new mast extrusion is considerably lighter than the original mast, and even tapers near the top too. So with a taller rig, longer boom, but overall lighter, and being conservative with a mainsail that perhaps doesn't use the entire length of the boom for its foot, I can avoid over-powering or excessive heeling, while still making the boat a little softer

It'll require relocating my traveler from the bridge deck just aft of the companionway into the cabin to avoid mid-boom sheeting. I may not be able to do complete end-boom, but I should be able to go at least 3/4 and gain that extra leverage. I have an extruded aluminum arch that may work for the traveler. I'm examining it from multiple angles to see if it is sturdy enough for mainsail loads. If I can make that work I should be able to do an overhead traveler that doesn't require the helmsman to leave the helm. I know purists think arches are ugly. (shrug) I don't care. I'm only concerned with whether or not it makes the boat more functional and safer or not.

[Mary Mac]

I believe that the 34-III has more ballast than previous models. 4,650 lbs in the 34-III and 3,750 lbs in previous models.

[thebastidge]

I'm guesstimating from the tube size (5.5" x 9" and 160 mil thickness) and length 41.75 that the original mast extrusion weighs about 205 lbs. That's if all my metric/Imperial conversions and an estimate using this chart for comparison holds up : whalespars.com/ (hitting the mast and boom link, I split the diff in weight/length of the WS 207 and WS 235 spars.)

My replacement spar is a Kenyon 4270: https://www.rigrite.com/Spars/Kenyon_Spars/4270-HP.php It is 3.7 lbs/ft. It's 51' long as-is. So 188 lbs or so. But I also need to cut it down to a usable length because it is right about 10 feet longer than the original and that doesn't seem wise. I figure on taking about 8' off the bottom (it was a keel-stepped mast on the J35, and will be deck-stepped on the Cal.) That takes about another 30 lbs off, so make it close to 50lbs or nearly 25% lighter than the original. Maybe a bit lighter than that, because it also tapers towards the top. But it has dual spreaders instead of single, and they're these airfoil spreaders at about 1lb/ft https://www.rigrite.com/Spars/Kenyon_Sp ... irfoil.php.

[Mary Mac]

I'm no engineer, but I think that the loading that the sail creates with lift forces would be far more significant than the weight of the mast.

You're going to get a larger sail area (potential lift) with the boom being longer. Where I live, it gets windy and I reef often, so more mainsail area doesn't sound appealing.

If you have a larger sail area because you add a longer boom, would the larger area cause the boat to heel over farther before the sail stalls or reduces lift? Maybe it doesn't matter or you can do other things to adjust?

The hull may be the same, but the length of the boom was changed on the 34-III at the same time as the ballast was added and the mast was heightened. I think a taller mast would affect the righting moment in a positive way..

Hopefully someone with a good understanding of this can chime in.

[thebastidge]

Correct about the loading due to more sail area. I definitely could over-power the boat with too much mainsail area. It's definitely a concern during this design exercise. That poses a danger to rigging integrity, for knocking down the boat, etc. Stability of the boat is a bit complex, relying on both the shape of the hull to increase buoyancy as it heels, the ballast to counter-act heeling force on the mast, and some bit of lift on the rudder to counter-act leeway and to some small degree, heel. Keel shape and even active mechanical designs may also provide lift to counter-act leeway and heel.

This design may mean needing to reef earlier, more often, and more reduction (i.e. go to second or third reef point rather than first reef point). Depending on sail foot and overall height, the aspect ratio of the sail changes. A high aspect ratio sail (long and skinny) creates more lift with less drag than a wider, shorter sail, just like wings. Reefed sails sacrifice sail shape, aspect ratio, and therefore lift efficiency. So tall skinny sails with less overall sail area still power better than more sail area on a wider sail when going to wind. Something to consider. A broader sail works better sailing straight downwind by just being a bigger bucket to catch air in.

But for my weight discussion, what I was getting at is taller= longer lever arm. When it's in column straight up and down, there is far more pressure exerted on the deck from the shroud and stay tension than from the weight of the mast. When heeled over a bit is when weight aloft comes into play. A small weight at the end of a 40+ foot lever (including the weight of the lever itself) exerts a lot of force.

So the extra ballast weight was probably added as a compensation for that taller mast among whatever other reasons they may have had for more ballast. Now, a sailboat without a mast, and all that ballast way down low, gets very "Stiff". The weight of the mast and gear aloft moderates how quickly the boat can snap back upright after rolling a bit, and the mast also has enough inertia to carry past the center line, slowing the roll and keeping the boat from harsh motions. I've heard that people often get motion sick on dismasted sailboats. A Mk III which got a Mk I mast and boom would probably be a very stiff boat indeed. Aspect ratios generally seem to have increased on later model sail boats in general. For example, I just looked up the Cal 31 (produced from 1979-1984) for another member on this forum and the I dimension (mast length) is nearly the same as the 34 Mk III, and the E dimension (boom length) is 13.5' or nearly as long as the Mk I. So it's considerably larger sail area, at relatively low aspect ratio, on a shorter boat than mine, with almost 1000 lbs less ballast and the same beam, and nearly the same LWL.

I also don't have to use the complete boom length. If I use a shorter-footed sail, like 12', and have 2' of bare boom end, I'm not being super efficient with weight, (especially when that extra 2' of aluminum is directly out over the side). It adds the very dangerous possibility of dragging the boom in the water if heeled over a lot. It may also affect sail shape if the boom outhaul has a lot of play in the line rather than taking the clew of the mainsail straight to the outhaul. That's something I don't have enough experience to determine with confidence. But on the other hand.... this is the boom I've got. And given that the same hull shape with less ballast had that length of boom, I think everything else can be dealt with and compensated for as the rig gets put together. Maybe I just can't point as high with the longer boom.

I just picked up a main sail from the Sea Scouts. This is something I didn't have before- I got a furling jib with the boat, but that was the only sail I had. The sail came off a C36, and the dimensions are Foot-11’5” Luff-37’7” Leach-39’10”. The price was right ($95) and I figure it's always good to have a spare if I find a better one within my price range. This one will need new slugs, there are a couple missing and the remaining slugs are plastic, cracked in some cases, and pretty weathered and beat up. The sail still has some amount of crispness, I'm not experienced enough to really gauge quality, but the scouts judged it in "fair" condition and they're pretty reliable.