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Sunfish boom on a Hobie 18? Kinda like the Tiger's boom?
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Author:  RobPatt [ Sun Jun 10, 2012 4:06 pm ]
Post subject:  Sunfish boom on a Hobie 18? Kinda like the Tiger's boom?
I put a spin on my boat and I'm thinking to try something else new.

The Tiger and lots of other cats have small booms, not the barbell monstor that the Hobie 18 has...

I was thinking of trying a sunfish spar as a boom, strong and lightweight.., and just minus the outhaul.

Thoughts on that? (I'd also thought about "splicing" some H18 dagger boards together to get one about 10 inches deeper...but not sure that'd let me point any better.. think it'd just be more drag..I digress... ))

Cheers, Rob.
Author:  BrianCT [ Sun Jun 10, 2012 4:31 pm ]
Post subject:  Re: Sunfish boom on a Hobie 18? Kinda like the Tiger's boom
Interesting thought, Rob. I'm not all that familiar with Sunfish but I do know the boom doesn't connect to the mast with a pin like it does on a Hobie. My Laser boom does and it has the requisite inner sleeve, but I'm not sure you'd gain much of anything converting to a Laser boom. It's fairly large in diameter compared to the modern F18 boom. I can tell you a Laser boom is just under 9' in length. I think the H18 boom might be a tad shorter, so it might work. Let us know what you decide.
Author:  Bacho [ Mon Jun 11, 2012 6:14 am ]
Post subject:  Re: Sunfish boom on a Hobie 18? Kinda like the Tiger's boom
You could do it with the correct gooseneck. I think you would also need to modify your clew plate for a strap.
Author:  srm [ Mon Jun 11, 2012 6:43 am ]
Post subject:  Re: Sunfish boom on a Hobie 18? Kinda like the Tiger's boom
I doubt the boom will be strong enough. Here's the problem that I see...

If you look at the boom/clew configuration on the Tiger mainsail, the boom actually passes through a webbing loop sewn into the clew of the mainsail. The main blocks connect directly to this webbing loop. Adjustment of the outhaul results in the clew AND the main blocks moving along the boom. This means that the mainsheet load is always directly in line with the leech of the mainsail. The boom operates purely as a compression tube.

The configuration on the H18 boom is different. The main blocks mount about 8 to 12" forward of the clew fitting. This means that the mainsheet loads and the clew loads are not in direct alignment and so the boom is in both compression and bending. The H18 boom profile is basically a tall thin rectangle and is therefore capable of resisting this bending load. The Sunfish boom on the other hand is a small circular cross-section. I suspect that with the high mainsheet loads on the 18, it would break. If it didn't break, at the very least, it would probably bend to the point that your outhaul setting would get all screwed up.

As far as the daggerboards are concerned, I think you're absolutely right about just adding more drag with no significant increase in lift/pointing ability. The 18 dagger boards are extremely low aspect by today's standards. You would be better off picking up a set of modern F18 dagger boards and building a sleeve that allows them to be adapted to the H18 dagger board trunk.

sm
Author:  John Lunn [ Mon Jun 11, 2012 6:52 am ]
Post subject:  Re: Sunfish boom on a Hobie 18? Kinda like the Tiger's boom
With a simple boom, would you lose the outhaul and rotator adjustments?
(does a smaller boom have the strength to handle those stresses?)
As I recall, the Tiger does not have an outhaul....someone please confirm.

In terms of the daggers, we have a shop here in Ottawa that specializes in building and repair of foils....
Competition Composites Inc....
they are building the centreboards and rudders for the new Gunboat 55.
Try http://www.fastcomposites.ca

Earlier this year, I thought of routering out a slot in an existing H18 dagger,
and epoxying in a Tiger dagger inside that slot.
Deeper board, more lift etc.
Better sailors than I pointed out that the skill (or lack of skill) of the skipper is far more meaningful than a touch of extra lift.
Doesn't mean I haven't stopped thinking about it.
Right now, I'm focusing on the 'lack of skill' bit....ha ha...
Author:  RobPatt [ Mon Jun 11, 2012 2:15 pm ]
Post subject:  Re: Sunfish boom on a Hobie 18? Kinda like the Tiger's boom
Yup... I was kind of guessing that if it failed it may be up near the front 18 inches or so, or maybe a bit further back...

I haven't had the chance to really look at how the tiger and other F18s attach the blocks, etc..... but yeah, if the stresses are lined up properly everything is handled well.

Nothing wrong w/the H18, and you gotta love that it's got the green man inside (the Hulk)... the boom, et al is just another part of the heavy duty SUV 4barrel V8 that the boat is... :-) she's a honkin whaler that races well too!

Not to mention when folks on the beach w/F18s, NACRA 20s and F18HTs are always breaking this or that... the H18 "timex" boat just takes the licking and keeps on tackin...

and the spin now is my turbo downhill machine... 'except I did find a hairline crack or two that weren't there before... not before I stuffed the bow to the crossbar w/a guy on the wire behind me.. oh well... sail it hard and when her time comes I'll deal w/it... but otherwise a very solid and good shape 1993 boat... w/the SX reenforcements all around too... cheers, Rob.
Author:  srm [ Mon Jun 11, 2012 4:11 pm ]
Post subject:  Re: Sunfish boom on a Hobie 18? Kinda like the Tiger's boom
RobPatt wrote:
Yup... I was kind of guessing that if it failed it may be up near the front 18 inches or so, or maybe a bit further back...


My prediction is that the sunfish boom would break right where you mount the main block hanger- this would be the point of maximum deflection and maximum stress.

If you had a high-aspect main where the clew doesn't overhang the rear crossbar (like on an F18), this style of boom will work. On the H18, the clew sticks out too far to make this system feasible.

sm
Author:  Daver [ Thu Jun 14, 2012 9:31 am ]
Post subject:  Re: Sunfish boom on a Hobie 18? Kinda like the Tiger's boom
Don't know about the sunfish boom. We made a boom from an old dinghy mast section. Absolutely fantastic sail shape in low to medium wind. Compared to the tiger boom it was almost 2.5 mm thicker.

High wind you will not be able to depower, the boom will just bend upwards again giving good sail shape but not what you want.

Pulling more on the downhaul just pulls out the rivets in the head of the sail, leaving you with a fully powered up sail in a 25 knot breeze.

The reason for the standard boom is to allow mast bend - you will not achieve that with a round or smaller boom.

The 18 mast is substantial, with bag up I have abused it to no end, from 20 to 25 knots of wind you must be careful with what you do - you do not want to lose your "backstay" if the boom decides to break. There are huge loads on the mast with the bag up.

Look at photos of F18's with bag up and see how the mast goes into an "s" shape etc. I still believe the 18 mast will take it whereas with a tiger your credit card goes into overdraft, or you buy the 2 piece mast insert.

The tiger has an outhaul, we copied that system for our boom - all fittings from the 18 boom was fitted.
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