Thread: Installing a boom vang

G'day Darce

Unless you double the purchase of your vang to compensate for the mechanical
disadvantage, and your lower mount is robust enough to take the doubled tension,
I doubt you'd be much better off.



Can you post higher res pics of the base of your mast? It might be possible to get
45 degrees to a slightly higher point on the mast with all-round lower tensions &
stresses for a reasonably workable result. Also, what sort is the boat, how long/wide,
how big is your mainsail, and how long is the foot ?

cheers
AJ

Originally Posted by b.o.a.t.

G'day Darce

Unless you double the purchase of your vang to compensate for the mechanical
disadvantage, and your lower mount is robust enough to take the extra tension,
I doubt you'd be much better off.

Can you post higher res pics of the base of your mast? It might be possible to get 45degrees to a slightly higher point on the mast with all-round lower tensions &
stresses for a reasonably workable result. Also, what sort is the boat, how long/wide,
how big is your mainsail, and how long is the foot ?

cheers
AJ

She is a 23' LOA 7'9" Beam shelter cabin knockabout designed by William Atkin in 1954. I have a couple of pics here

At the moment I have only the main sheet on a free traveller to control shape of the sail. (This is an old boat, remember )Her original 24' wooden mast was lengthened by 3 meters in 1961 when it was replaced by alluminium. I haven't measured as yet, but the plans called for 145 sq ft in the main. She retains her 12' 9" boom.

If I go to a higher point on the mast to achieve the 45° I'd be bringing the attachment point on the boom closer to the mast as well. Wouldn't that thefore reduce the lever arm on the boom itself, subsequently increasing the force required to achieve the same effect as felt by the clew? If that is the case, then I'm also placing greater stress on that portion of the boom. Seeing as how the boom is wood and the mast is alluminium... I was thinking I'd be better placing the stress on the mast.

I'll get some better piccies tomorrow, weather permitting - it's forecast for thunderstorms here in Perth

tweaked earlier reply/query & added pic.

T'storms ?!!! We should be so lucky. Can barely remember what rain looks like in
Adelaide. I see the east coast copped a fair old pasting tonight.

cheers
AJ

Add my two cents, with the wooden boom, limited space, how close
the boom is to the deck, cabin in the line of attack.

The boat has run for over fifty years without a vang, I would spend
my money on something else.

Originally Posted by b.o.a.t.

tweaked earlier reply/query & added pic.

T'storms ?!!! We should be so lucky. Can barely remember what rain looks like in
Adelaide. I see the east coast copped a fair old pasting tonight.

cheers
AJ

We had our thunderstorm last night, what a ripper! We even had hail!

I might be missing something here. In the pic you've moved the attachment points as indicated by the blue which I thought would be providing a shallower angle. I like the fact this moves the lever further along the boom, but I would think I'd have to go more than 4:1 to see any benefit.. although I guess anything is better than nothing.

Papa, the reason I want a vang is because I'm racing. It's only jib & main, but I want more control over the sail shape than I currently have with main sheet only. This little beauty has quite a fast hull for her age - she surprised quite a few of the boys down the club.

Howdy,

A boom vang is VERY useful. It will increase the performance of the boat considerably on most points of sail and also reduce the risk of accidental gybing when running or broad reaching. A powerful system also reduces most of the load on the mainsheet when going to windward.

Poorly used it can increase the rare risk of breaking the boom if the boat rolls heavily and boom drags in a sea when running at high speed. But this is very rare.

There is a misconception here ... whatever angle the bottom part takes ... wherever the projection of that angle intersects the boom ... then that is your effective location .. so don't worry about the cat's cradle you are trying to use at the top - it doesn't make any difference.

There are two normal ways of dealing with the problem.
1/ move the vang attachment on the mast up from the deck level. It would be nice to see a gap of about 2ft between the vang attachment on the mast and the gooseneck ... if it can be more then great!. And then the attachment point on the boom could be about 3ft back from the gooseneck a bit less is ok.
2/ or like Papa says .. accept the performance disadvantage and be more careful when sailing square and you can have 50 years of VERY satisfying sailing.

A vang needs to be quite powerful as do the attachment points to the spars. In your size you could have 3:1 at the mast and lead it back to a jammer and tension it with the halyard winch (assuming you have one at the front of the cockpit.

If a winch is not practical I would do a 2 to 1 cascade system. This looks like this one here ... which is too complicated for what you want.



Use block 1 and 2 as they show ... then three can be a single block too. The bottom end attachment needs to be on the mast (not beside the mast as they show here - they will break their gooseneck or something with this system in the diagram). For the basic system you need a single block with a becket.

Don't let them talk you into ball bearing blocks ... not necessary and counter productive for a cruising system - the balls get squeezed flat because things are not moving around much on a long trip.

Might need another pulley on the front end of the cabin to lead the control back to the cockpit. If it is only a small deflection there you could just put a brass strip for the line to rub against (neatly countersink any fastenings and sand the holes smooth so they won't cut away at the line)

This gives you an 8:1 system - If you were racing ... I would set it up with a three or four to one at the bottom (the part from block #3) to give about 12 or 16 to one.

Cascade type systems (this type of rope layout) are generally the cheapest way to go because they require far fewer blocks - but make sure your rope is small enough for good clearance as it passes through. For example a 5mm spectra line would be plenty strong enough and have less friction from passing through the blocks cleanly.

Best wishes
Michael

You also don't have to have the vang mounted at the mast, it can be on the cabin top. This typically means a track mounted car, so you don't have to adjust it each time you adjust the sheet. This is often a race setup, using a curved track. This will eliminate the problem of fouling the cabin front, of course at a greater cost.

If you're a casual cruiser and not interested in constantly adjusting shape (like racers do) then your vang doesn't need to be much (as Mik has mentioned). It could be something as simple as a tackle left dangling from the boom and attached to a sidedeck pad eye when the sheet is well freed. On an old gaffer, I used to own, this was the set up I used, except I had two tackles, one for each tack and they were attached at the rail. When I knew I was to reach off for a while, I'd snap on the tackle that was on that side. You also can get a much better purchase this way, pulling down nearly vertically on the boom, which is easier, requires less falls and blocks.

The vang can be pretty much anywhere on the forward half of the boom to be effective. The more downward pull you can generate, the more efficient it is and the less tackle you need.

Hey Darce,

that's a nice looking boat -real sweet lines. Looks like you have a bit of work to do to the deck though

How long have you had her, and what can you tell us about her history?

Looks like you have her on a mooring in Mangles Bay - do you race with TCYC?

Mike

Originally Posted by MikeyRoberts

Hey Darce,

that's a nice looking boat -real sweet lines. Looks like you have a bit of work to do to the deck though

How long have you had her, and what can you tell us about her history?

Looks like you have her on a mooring in Mangles Bay - do you race with TCYC?

Mike

Mike, I've had her for about a month now. I picked her up from a bloke who'd decided she was beyond his idea of repairable. I reckon she's too pretty to strip down so I intend restoring her after sailing her through summer.

There's quite a bit of work to do on her; the plywood deck is going and will be planked, about 80% of her frames will need to be replaced so all her furniture (mostly deteriorating ply as well) will be stripped out, there's a small section of dry rot which needs chasing too. Seeing as how I've got all that out I may as well replace the keel bolts and straps. In fact I don't like the look of the ally mast so that'll be replaced by a nice new wooden one.

She is indeed moored at Mangles and I have joined TCYC and raced with her once in the Jib and Main. What a hoot. I'll continue to race her over summer - weather, crew and seaworthyness permitting