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Adjustable raking systems

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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 20 at 12:51pm
Raking the rig moves the CoE aft, useful to balance with a raked centreboard for stronger winds. Moving the foot of the mast while leaving the shrouds and forestay fixed (effectively pivoting the rig around the hounds) would move the CoE forward by a smaller amount. AFAICS there are both similarities and differences between the effect moving the mast foot has on windsurfer and dinghy rigs but in both cases it comes down to balancing the rig CoE to the hulls CoLR. On a Raceboard we move the mast foot aft offwind and retract the CB so the CoLR is wall back under the straps for minimal wetted/planing area, upwind we want as much WL as possible so move the rig forward about 18".

Edited by Sam.Spoons - 17 Nov 20 at 12:54pm
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Post Options Post Options   Quote Grumpycat Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 20 at 1:45pm
Re the supersofa . I thought they only have adjustable forestay and lowers . So not really what your looking for . Sure mr spoons  will put me right  Smile
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 20 at 2:14pm
Originally posted by Sam.Spoons


Raking the rig moves the CoE aft, useful to balance with a raked centreboard for stronger winds. Moving the foot of the mast while leaving the shrouds and forestay fixed (effectively pivoting the rig around the hounds) would move the CoE forward by a smaller amount. AFAICS there are both similarities and differences between the effect moving the mast foot has on windsurfer and dinghy rigs but in both cases it comes down to balancing the rig CoE to the hulls CoLR. On a Raceboard we move the mast foot aft offwind and retract the CB so the CoLR is wall back under the straps for minimal wetted/planing area, upwind we want as much WL as possible so move the rig forward about 18".


Yep, I know all that, what I don't know and am always weak with is pulley systems.

And what the relationship should be for example between the fore stay and lowers/shrouds.

Edited by iGRF - 17 Nov 20 at 2:14pm
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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 20 at 2:26pm
Originally posted by iGRF

Originally posted by Sam.Spoons


Raking the rig moves the CoE aft, useful to balance with a raked centreboard for stronger winds. Moving the foot of the mast while leaving the shrouds and forestay fixed (effectively pivoting the rig around the hounds) would move the CoE forward by a smaller amount. AFAICS there are both similarities and differences between the effect moving the mast foot has on windsurfer and dinghy rigs but in both cases it comes down to balancing the rig CoE to the hulls CoLR. On a Raceboard we move the mast foot aft offwind and retract the CB so the CoLR is wall back under the straps for minimal wetted/planing area, upwind we want as much WL as possible so move the rig forward about 18".


Yep, I know all that, what I don't know and am always weak with is pulley systems.

And what the relationship should be for example between the fore stay and lowers/shrouds.

I know you know all of that but I guess others will read this thread who don't.


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Post Options Post Options   Quote Sam.Spoons Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 20 at 2:27pm
Originally posted by Grumpycat

Re the supersofa . I thought they only have adjustable forestay and lowers . So not really what your looking for . Sure mr spoons  will put me right  Smile

Dear aunty marge....  LOL

We probably need the input of a proper boat designer here

But, that Supernova has, as you say, forestay and lowers adjustable, mine had just a forestay, I don't recall but I don't think they are allowed adjustable shrouds.


Edited by Sam.Spoons - 17 Nov 20 at 2:32pm
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Post Options Post Options   Quote Rupert Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 20 at 2:44pm
There was an unstayed trapeze boat in the late 80s, called the Delta (or Delta4?). The mast was the size of a tree trunk at deck level. I'm sure with modern materials it could be done better, but I see all sorts of rig control problems.

Maybe a mast stump to spread the deck loadings? An adjustable one...

Edited by Rupert - 17 Nov 20 at 2:46pm
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Post Options Post Options   Quote Old bloke Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 20 at 3:23pm
I think you need to work out what you want the lowers to do as you rake.If you want the tensions v the uppers to remain the same then the calculation is easy. If though you want more bend as you rake the I would experiment with holes and pins before trying anything clever/expensive.
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Post Options Post Options   Quote H2 Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 20 at 4:10pm
Do you really need lowers? The mast is deck stepped so the distance from gooseneck to the bottom of the mast is relatively short and could easily be made shorter if you were going to change the rig anyway. On the H2 there was lots of noise about lowers when the boat came out but we soon realised the rig did not need them for this same reason and we have an adjustable forestay to adjust rake / rig tension on the fly. Might be easier to get the boat up and started without them.
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Post Options Post Options   Quote iGRF Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 20 at 5:36pm
Correct me if I'm wrong here but I'm assuming other than use as a rigging aid the key use for lowers is to combat kicker induced lower mast bend. So, following that logic then the desire would be rake with neutral effect on lowers tension which mean as the rig rakes back they need their tension increased. Whereas, if the whole lot were sliding forward (ike someone mentioned back there with forestay sliders) in order to rake the mast fromthe foot then it would seem easier to have an arrangement where they all moved in concert, even leaving the forestay not necessarily needing much adjustment, hence my thinking...
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Post Options Post Options   Quote Granite Quote  Post ReplyReply Direct Link To This Post Posted: 17 Nov 20 at 7:42pm
The lower shrouds allow you to controll the lower mast bend. You are correct that they oppose the kicker, and their length and resting tension plays a role in how much the lower to mid mast will bend as the kicker is increased.

For the sliding foot I am unsure exactly what you want to acheave and that will alter how you design it.

If you want to move the foot fwd change the rake of the mast. Then I think it could be done with a track attached to the foot of the mast and bent to the same radius as the distance from the foot to the hounds. Provided the center of the circle of the track points at the hounds, you don't have spreaders or lowers then you should be able to move the foot without altering rig tension significantly.
Adding lowers into the mix as a single string adjustment would be tricky as I don't think the relationship would be linear, so it would be hard to set the ratio.

If on the other hand you want to move the mast back and fwd but keep the rake the same. Then I think you would need a Y shaped frame. This would be attached to the hull with tracks at the shrouds, forestay and mast foot. The whole frame would keep the alignment between each part and would slide back and fwd.
You could build a raking tension sysem onto that frame provided all the anchor points for the various purchases were attached to the frame. The setup would be the same as for a normal raking system.

I think it would be hard to do either without adding a lot of weight or requiring compromise in other areas.



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