Raising a boom

[pandos]

One of the few gripes I have with my boat, a HR352, is that the boom is at head height.

This means no Bimini and constant danger when going down wind...(reduced but not eliminated by a preventer)

I was just reading a blog by a guy who had his raised by about 250mm (10 inches). He referred to losing area from the bottom of the mainsail.

It set me thinking about doing this, I presume all that is needed is a new mast fitting and a bit of sail chopping...

But why not lose 10 inches from the top of the sail? Rather than the bottom?.

Also would raising of the boom damage stability in any meaningful way.?

 

[Laser310]

if you lose the sail area at the top, you will have a square top main, and may have a problem with the backstay while gybing or tacking.

even if the center of effort of the sail plan moves a bit higher, the loss of sail area will mean that you will have less heeling moment at full sail for equal wind strength compared with the original sail plan.

i think this problem with a low boom is just inherent in boats under say 40ft.., and even on many boats larger than that.

i don't know the HR 352, but i will guess it is not a particularly powered-up boat and i doubt you want to lose any of the power you have.

 

[William_H]

You may be able to crib a bit of extra height of the boom aft end without resorting to cutting the main sail. Firstly look at mast rake. You may be able to shorten the fore stay to tilt mast forward a little.
You may find you have room at the main sail luff top where you can raise the sail a little more. If so and you have a loose footed main you fit a shackle or spacer so that tack can rise a bit. Remove the tack attachment and hoist sail up until the top hits the mast top sheave. NB You need some extra space at top for stretching the luff.
You might have or can get fitted a "flattening reef" this is an eyelet in the leach about 25cms above the clew eyelet. This can be hauled down to the boom to take out the camber at the bottom of the main sail. So lifting the boom by that amount.
However all these tricks only lift the aft end of the boom. The gooseneck will remain fixed at the same height above the cabin top. To raise the front of the boom you will need to remove and refasten the goose neck attachment up higher. In doing so you will find the luff of the main sail too long.
You could cut off the top of the main sail. This as said will make the sail flat topped. This may not fit inside the back stay. Or you could cut down along the foot of the sail.
You need to hoist the main sail and check clearances head to top sheave and top of sail to back stay with binoculars before making any decisions. ol'will

 

[pandos]

The top of the sail can be altered to suit the backstay.. I had this done in the past and I can see no reason why it cannot be done again. I think I have a few inches already at the top so probably not a huge job.

As suggested the boat is not particularly powered up, but it carries sail well in any kind of a blow so I would be more worried about raising the center of effort...but probably not worried enough to throw away the bottom of my mainsail permanently..Realistically if it was a big problem I could reef earlier..

The boat I referred to would have a taller mast so had more sail area to begin with but also a higher center of effort...

Can it just be a case of drilling off the old mast bracket, fitting an aluminium plate using the existing holes and a dose of sikaflex.
And putting the bracket 10 inches higher?

(I like the idea of removing the existing bracket unless I discover chunks of mast have been eaten away by corrosion...)

Hallberg Rassy 352 Freyja - Maintenance & Upgrades

 

[Laminar Flow]

For what its worth, you could cut a substantial part off the top of a sail and not notice the slightest reduction in performance. There is so much turbulence behind the (untapered) mast that the top portion is entirely ineffective in any case.

In regards to "raising" the CE by moving the boom up 10": you can easily do the math on that and you would find out that it is entirely negligible.
The loading for a rig is assumed at 1lbs/sqft (4.88kg/m); accordingly, you would be reducing the wind load by 12lbs or thereabouts, countered by raising the boom 10"?

I would presume that neither you, nor anyone else would be able to detect the slightest difference in performance whatsoever, even if you were to race side by side with an unmodified model.

 

[pandos]

For what its worth, you could cut a substantial part off the top of a sail and not notice the slightest reduction in performance. There is so much turbulence behind the (untapered) mast that the top portion is entirely ineffective in any case.

In regards to "raising" the CE by moving the boom up 10": you can easily do the math on that and you would find out that it is entirely negligible.
The loading for a rig is assumed at 1lbs/sqft (4.88kg/m); accordingly, you would be reducing the wind load by 12lbs or thereabouts, countered by raising the boom 10"?

I would presume that neither you, nor anyone else would be able to detect the slightest difference in performance whatsoever, even if you were to race side by side with an unmodified model.

Thanks for that...maths and physics are not something that I have any in-depth knowledge of...(I have no interest in acquiring any either)

The thought of not being in danger of having my head removed and of having a decent bimini is making me smile already....

 

[CAPTAIN FANTASTIC]

You could adjust the topping lift to gain a few inches; cutting a few inches from the top of the main is not a problem at all, you are only cutting it by 250 mm . You never notice any impact on performance. As a last resort, you could relocate the gooseneck, I did this recently when I replaced my boom. I too dont like the boom close to my head!!!

 

[CM74]

It might be worth having a look to see if the main is currently going all the way to the top of the mast - my main halyard is too thick and has a splice so thick that there's scope for the main to go up about 200mm more. The splice is so thick it jams in the block at the masthead.
(The gooseneck is on a slide that makes it easy to adjust boom height)

 

[Graham_Wright]

Raise the mast? The boat next to mine has an obvious extension towards its foot.

 

[dunedin]

It might be worth having a look to see if the main is currently going all the way to the top of the mast - my main halyard is too thick and has a splice so thick that there's scope for the main to go up about 200mm more. The splice is so thick it jams in the block at the masthead.
(The gooseneck is on a slide that makes it easy to adjust boom height)

Definitely worth taking some photos of the top of the mast with the sail up - preferably with a telephoto lens from a decent distance away (eg in a dinghy or along the pontoon)

This will show any opportunity simply to hoist the sail higher, and importantly how close the sail goes to the backstay currently.

PS I would take with a BIG pinch of salt some of the suggestions on here of "shortening the sail at the top". Unless do proper fat head sail with extra batten at top the leech won't hold its shape - and a fat head sail will almost certainly jam on the backstay unless on a boat designed for this from the outset. Shorten from the bottom.

 

[dunedin]

Raise the mast? The boat next to mine has an obvious extension towards its foot.

Some boats like the Fulmar bizarrely had a mast joint six feet or so above deck. Almost like Westerly had a bunch of wrong ordered masts lying around for smaller boats and decided, "sod it,they will do" and stuck an extra bit on the bottom.
NB Never heard of any actual problems, so the extension must be pretty solid

 

[pandos]

Some boats like the Fulmar bizarrely had a mast joint six feet or so above deck. Almost like Westerly had a bunch of wrong ordered masts lying around for smaller boats and decided, "sod it,they will do" and stuck an extra bit on the bottom.
NB Never heard of any actual problems, so the extension must be pretty solid

This was not just a Westerly trick. Hallberg Rassey did the same with mine, and many others of the same vintage which I have seen.

My proposal is not about stretching the mast. Just shifting the boom upwards by about 10 inches.

However your post brings to mind the possibility that the sleeve at the join is a backing plate for the gooseneck fitting!

 

[DownWest]

You might want to check the height of the gap in the sail track where you feed the slugs in before raising the goose neck?

 

[anoccasionalyachtsman]

Some boats like the Fulmar bizarrely had a mast joint six feet or so above deck. Almost like Westerly had a bunch of wrong ordered masts lying around for smaller boats and decided, "sod it,they will do" and stuck an extra bit on the bottom.
NB Never heard of any actual problems, so the extension must be pretty solid

I don't know who supplied their masts, but Kemp used to have a 40ft max tube length, others may have been longer/shorter, but because the sleeved joint is stronger than the bare tube, and putting it at the gooseneck area where the greatest stresses are found is a common practice. (Not that that rules out the 'pragmatism of production' you suggest).

 

[Laminar Flow]

PS I would take with a BIG pinch of salt some of the suggestions on here of "shortening the sail at the top". Unless do proper fat head sail with extra batten at top the leech won't hold its shape - and a fat head sail will almost certainly jam on the backstay unless on a boat designed for this from the outset. Shorten from the bottom.

The HR has a masthead rig with fixed backstays. So there is no possibility of a "fat head" main.
The top 15% of a triangular main does absolutely sweet nothing, aerodynamically speaking, due to mast interference and induced drag.
Altering the top of the sail is a lot easier than cutting 10" off the bottom, especially if the sail is not loose-footed.
Also, cutting off the top you might lose 1 sq/ft; at the bottom you lose 12 sq/ft, if that makes any difference.
As the OP is suggesting to reduce his boats luff by a mere 2.5% by raising the boom a few inches, I think we should all come to our collective grips in regards to how little that means in practical terms and as long as the boom clears the backstay there is absolutely no reason to shorten it.
Equally impractical is the suggestion to raise the mast, as this would entail all new standing rigging and major modifications to the spar.

 

[pandos]

As the OP is suggesting to reduce his boats luff by a mere 2.5% by raising the boom a few inches, I think we should all come to our collective grips in regards to how little that means in practical terms and as long as the boom clears the backstay there is absolutely no reason to shorten it.

Its a center cockpit so no issue with the boom and backstay.

Another huge advantage will be vision ahead when motoring as there will be a slot at head height above the spray hood and under the boom...

I think time for proper examination of the mast tomorrow....

Just had an email from the guy that inspired this idea and it seems it was as simple a job as it looks, the boom bracket was bolted in place and the riggers who did his work just tapped the mast in the new position and used new bolts with blanking bolts threaded into the original holes.

Thanks for all the replies...

 

[jwfrary]

Its a center cockpit so no issue with the boom and backstay.

Another huge advantage will be vision ahead when motoring as there will be a slot at head height above the spray hood and under the boom...

I think time for proper examination of the mast tomorrow....

Just had an email from the guy that inspired this idea and it seems it was as simple a job as it looks, the boom bracket was bolted in place and the riggers who did his work just tapped the mast in the new position and used new bolts with blanking bolts threaded into the original holes.

Thanks for all the replies...

Using rivnuts for the threaded fittings is probably a better way than just a tapped hole in the Ali section which will have little resistance to pulling out.

 

[pandos]

Using rivnuts for the threaded fittings is probably a better way than just a tapped hole in the Ali section which will have little resistance to pulling out.

I went to the boat yesterday and also received another photo from the guy that has already done this on a similar model.

The existing is riveted so I am going to replicate that approach.

Thanks again for the suggestions...

 

[jwfrary]

I went to the boat yesterday and also received another photo from the guy that has already done this on a similar model.

The existing is riveted so I am going to replicate that approach.

Thanks again for the suggestions...

An equally valid method of attachment.

Dont forget to use monel rivets and duralac!

 

[Fantasie 19]

But why not lose 10 inches from the top of the sail? Rather than the bottom?.

When I had some length taken out of the luff on my main, that was exactly what my sailmaker (Batt sails) did - it also means you retain more sail area...