Boom Height W.R.T. Cockpit Cover

[goeasy123]

How do I work out where my boom sits when under sail so that I can design the height of my new cockpit cover to give sufficient clearance?

I haven't got the old cover to compare. The boat is tucked up for the winter so I can't set the sail to find out. I thought I could just hoist the sail and pull the main sheet tight, but that pulls the boom too low 'cause the leech of the sail is curved, the sail is shaped and pulling on the mainsheet stretches a longer line from the clew to the head.

 

[Refueler]

My 25ft'r - the sprayhood frame is just less than horizontal boom ....

But my 38ft'r ... if I set at horizontal - then it would need a very low frame height. Some others of same boat as my 38 - the boom has been raised a touch on the mast runner to allow a sprayhood - this of course means a slightly shorter luff / leech mainsail.

 

[Neeves]

Forget the dimensions when you are 'sailing'. The dimension you need is defined by where the boom is when you reef, usually lower than when sailing. A twitchy boom in a sea when reefing can be lethal - at least to a sprayhood.

We restricted our boom by fixing its lowest point with the topping lift (and the topping lift was then 'fixed'). This allowed us to put in reefs with the low point of the boom fixed. You could make the same restriction with a solid vang (which we did not have). We were not designing a spray hood but a solid foam/glass helm station - but same idea.

Jonathan

 

[goeasy123]

Forget the dimensions when you are 'sailing'. The dimension you need is defined by where the boom is when you reef, usually lower than when sailing. A twitchy boom in a sea when reefing can be lethal - at least to a sprayhood.

We restricted our boom by fixing its lowest point with the topping lift (and the topping lift was then 'fixed'). This allowed us to put in reefs with the low point of the boom fixed. You could make the same restriction with a solid vang (which we did not have). We were not designing a spray hood but a solid foam/glass helm station - but same idea.

Jonathan

Good point, but I still have the problem of where the boom sits when reefed.

If we had a mark on the topping lift or a solid vang and we hadn't touched it after we took the old cockpit frame off we wouldn't have a problem.. But we have a gas rodkicker and we don't know what it's sail up setting it.

 

[rotrax]

Good point, but I still have the problem of where the boom sits when reefed.

If we had a mark on the topping lift or a solid vang and we hadn't touched it after we took the old cockpit frame off we wouldn't have a problem.. But we have a gas rodkicker and we don't know what it's sail up setting it.

You have just answered your own question......................

Re-fit the mainsail, reef, measure, add a bit 'in case' and Robert will be the name of your Fathers Brother

 

[dunedin]

Good point, but I still have the problem of where the boom sits when reefed.

If we had a mark on the topping lift or a solid vang and we hadn't touched it after we took the old cockpit frame off we wouldn't have a problem.. But we have a gas rodkicker and we don't know what it's sail up setting it.

No photos taken when sailing, which show the rod kicker under use?

 

[Neeves]

This is one of those threads where, as far as I can ascertain - we actually cannot help but give advice.

The answer lies in hoisting the main and measuring. Even if 6 of us had the same yacht our mainsails could all be slightly different resulting in different answers.

Jonathan

 

[goeasy123]

You have just answered your own question......................

Re-fit the mainsail, reef, measure, add a bit 'in case' and Robert will be the name of your Fathers Brother

The reef position under sail is different from the reef position when there's no load on the sail. So that won't work

No photos taken when sailing, which show the rod kicker under use?

Unfortunately not

This is one of those threads where, as far as I can ascertain - we actually cannot help but give advice.

The answer lies in hoisting the main and measuring. Even if 6 of us had the same yacht our mainsails could all be slightly different resulting in different answers.

Jonathan

Indeed, I'm finding the dialogue encouraging.

Hoisting the main and measuring is certainly part of the answer. The other part is getting the main under load, close hauled with the traveller positioning the boom on the centreline.

 

[dunedin]

The reef position under sail is different from the reef position when there's no load on the sail. So that won't work
…….
Hoisting the main and measuring is certainly part of the answer. The other part is getting the main under load, close hauled with the traveller positioning the boom on the centreline.

Slightly confused by these comments / concerns.

The boom will be lower (whether reefed or not) when the sheet is tensioned but there is no wind in the sail than it will be when filled with wind. But you need to allow height for the sail sheeted but not filled - eg if motoring in a calm.
And, as noted earlier, the boom is often lowest when hoisting sail or pulling a reef in.

Also amazed you have no photos under sail. We have lots just taking scenic shots when sailing. But as well as ave several hundred photos taken of every conceivable part of the boat stored and organised on the home PC, as a photo reference file. Photos of everything at the masthead are particularly useful to ensure got all the right stuff before heading aloft. Worth doing next season.

 

[MontyMariner]

Can you remember if you have to duck when you change tack?
That will give you a clue!

 

[goeasy123]

Slightly confused by these comments / concerns.

The boom will be lower (whether reefed or not) when the sheet is tensioned but there is no wind in the sail than it will be when filled with wind. But you need to allow height for the sail sheeted but not filled - eg if motoring in a calm.
And, as noted earlier, the boom is often lowest when hoisting sail or pulling a reef in.

Also amazed you have no photos under sail. We have lots just taking scenic shots when sailing. But as well as ave several hundred photos taken of every conceivable part of the boat stored and organised on the home PC, as a photo reference file. Photos of everything at the masthead are particularly useful to ensure got all the right stuff before heading aloft. Worth doing next season.

If I understand you correctly, I need to know the lowest point the boom on the centreline when under sail. I..e. close hauled, longest reef, sheet tight and traveller placing the boom on the centreline. (I know, an unlikely combination). That determines the clearance I have for the cockpit cover. The boom never needs to be lower than that. The gas vang will hold it above that and we lock the boom between the sheet and topping lift above that when motoring of stopped.
I have pics, but there's not enough detail.

Can you remember if you have to duck when you change tack?
That will give you a clue!

No. So it's at least higher that 5'10 3/8". But, by how much. Damn it!

 

[ashtead]

Surely the tent can be higher once the boom ends -I have seen this approach on a Bav34 tent so the boom clears the top of tent but rise as over the wheel. Many cockpit makers such as Tecsew have ideas on their website which might give ideas.

 

[goeasy123]

Surely the tent can be higher once the boom ends -I have seen this approach on a Bav34 tent so the boom clears the top of tent but rise as over the wheel. Many cockpit makers such as Tecsew have ideas on their website which might give ideas.

Center cockpit. It's all under the boom.

 

[Neeves]

I don't know, I assume none of us know, how you use your vang and the rod kicker. If you do not 'use' the kicker, other than to support the boom, and all adjustment is made by the vang, rope based, then you don't need to consider the main, at all. The low point of the boom is restricted by where ever the rod is fixed. And/or if when you reef you rely on the end stop of the kicker - that is your low point for the boom.

Just go to the boat, swing the boom amidships - and measure, go home.

But I may have this all wrong.

Jonathan

 

[goeasy123]

I don't know, I assume none of us know, how you use your vang and the rod kicker. If you do not 'use' the kicker, other than to support the boom, and all adjustment is made by the vang, rope based, then you don't need to consider the main, at all. The low point of the boom is restricted by where ever the rod is fixed. And/or if when you reef you rely on the end stop of the kicker - that is your low point for the boom.

Just go to the boat, swing the boom amidships - and measure, go home.

But I may have this all wrong.

Jonathan

The end stop on the kicker is way past the lowest sailing position.

However, an idential boat has just turned up 3 boats down in the marina. He's got his canopy up. So I'm going to go with that measurement plus a margin.

 

[ashtead]

Buy a habitent maybe but surely an owners website might be a useful source of info ?

 

[Pye_End]

The end stop on the kicker is way past the lowest sailing position.

However, an idential boat has just turned up 3 boats down in the marina. He's got his canopy up. So I'm going to go with that measurement plus a margin.

You won't want the boom clonking the sprayhood on the way past.

There may well be days when you will be motoring with the main hard in.

No 2 boats are ever identical - key dimension really need to be measured on your's.

Post 5, for me, is the answer. Measure with the sail up but unloaded.

Regarding reefs - the boom angle is not set in stone, and may well be the same or different from full sail, so you need to check this. You may well be able to reef with a different boom angle (slab reef) by putting say a soft shackle on the luff cringle, if that is your preference.

 

[davidmh]

The OP wants to make a cockpit cover. Is he going to sail with the cover in place?
If he is not sailing with the cover in place then he could top up the boom to any height when the sail is furled. I would opt to have the boom a bit above the horizontal to allow for any stowed sail that is below the boom.

David MH

 

[ashtead]

If he is clever he will have a top he can motor with and zip in sides and back with a connector panel between the sprayhood end and front of the canvas new roof then you have best of all worlds ie can motor with top up

 

[goeasy123]

If he is clever he will have a top he can motor with and zip in sides and back with a connector panel between the sprayhood end and front of the canvas new roof then you have best of all worlds ie can motor with top up

That's what we're doing....Ooh, apparently I'm clever!!