Light wind reacher on fixed furler.

[rotrax]

Island Packet offer an optional reacher on a solent rig.
For our boat, a heavy 12 metre Motorsailer, the SP Cruiser, light wind performance is poor. It has a self tacking jib on a Hoyt boom and an in mast furling main with a high boom as it must clear the pilot house roof.
15-20 kts true on the beam, hull speed. With tide we have averaged 8.5 kts for four hours in these conditions.
Trouble is, we dont get that all the time!
We are having a used but overhauled Facnor furler and Solent forestay fitted forward and parallel to the OE forestay soon. I have found the hardware, sheet blocks, furling line leads sheets, clutches and a winch - only need one, the OE powered one will work the Sheet/Furler on the Starboard side - and I have fabricated a bowsprit fitting. The masthead is already fitted with the top fitting.
I am confused about the best sail to order.
OE sails are 714 sq. feet.
After reading a bit Some suggest the reacher is used up to 15 kts true, wind in front of the mast.
Other writings say it can be used downwind.
Our use would be light wind conditions - with the boat as it is, it is not worth trying to sail in less than 10 knots true.
To be able to sail in light winds would be what we are aiming at.
What sail would be reccomended?

 

[TernVI]

I suggest 'doing the vectors' for pushing your '10 knots true' down to say 7 knots true.

But first maybe you need to be clear in your own mind what 'worth trying to sail' means in some sort of hard numbers.
To me it's woprth sailing if I can get where I want to go and enjoy pulling string and not have the engine on.
Other people want to make x-amount of progress, I won't say they are wrong.

My personal preference would be for the biggest asy kite you can hang off the mast.
You should be able to sail with the apparent wind maybe 30 degrees forward of the beam, which in 10 knots true should mean you can head reasonably low.
How low will depend on how much area, vs how much displacement.
For instance a 1000 sq ft asy will give you x-amount of drive in y knots apparent, which will give a boat speed of z.

Something that will go on a furler more comes into its own reaching higher in a bit more breeze.
You won't get massive area on that furler, or big fullness, so not huge drive downwind in light air.

But for sure, the biggest thing you can put on a furler is easy to handle, and a businesslike asy, even with a sock, is more demanding.

For a heavy cruising boat, a big conventional spinny is a good thing to have IMHO.
Big is the key, you want it for low apparent wind.

 

[rotrax]

Thanks for the reply, appreciated.

We are in our seventies and easy handling of the sails is essential. That is why we have the boat we have, one power winch handling all lines, small rig, but with 110 HP when the wind wont serve.

Island Packet are offering an optional reacher on a manual or powered furler on many of their models. The boats are unashamed modest rigged cruising boats, designed for a mature cruising couple with easy sail handling a priority.

I am waiting for a reply from the factory about sail dimensions. While reading about code zero/reachers I became confused as some suggest they are for use 30 to 90 degrees before the mast and other say they can be used for downwind sailing.

Perhaps they can do both?

It is clear our boat as it is will never perform well in light winds, too heavy and a small sail plan.

We are hoping adding a 750 ish sq foot reacher might allow more time under sail. ?

If we wanted a fast sailing boat we would not have made the choice of a motorsailer. Comfort alongside or on the hook plus easy on/easy off by the rear swim platform were a major part of our choice.

 

[ashtead]

We are a 12.8 m boat but perhaps at 9.8 tonnes not as heavy as an IP . If you look at specs for us on the moody site it sets a size for chute sail area. I have recent had a quote from Peter S in Lymington and some samples to consider. It might be worth contacting him or your preferred sailmaker on size and also weight-1.5 oz is often quote but you can have 0.9 for example. I don’t know if a problem for you but also need to consider how to fit the chute furler with whatever bow furlers you have to get clearance eg do you need a prodded pole by selden off bow for example. Like you we already have a self tacker jib and large headsail on furlers. Curious to know what size reacher factory suggest .

 

[TernVI]

....

I am waiting for a reply from the factory about sail dimensions. While reading about code zero/reachers I became confused as some suggest they are for use 30 to 90 degrees before the mast and other say they can be used for downwind sailing.
...

If you can get an estimate of how fast the sail will move the boat in say 6, 8 and 10 knots apparent, you can then draw a vector triangle and see where that's actually taking you relative to the true wind.
Only then can you see whether the 'downwind' component is useful.

My experience is that where we want to go is rarely 'dead down wind'.
The wind blows roughly but not exactly, along the coast quite often.
Then you have the fact that it shifts during most days.
Then you have the ability to 'tack' inshore and offshore to play the tides.

We have a pretty big cruising chute, in light airs we are often doing 6 knots with the apparent wind well forwards, and heading maybe 30 degrees up from dead down wind. So our vmg downwind is of the order of 5.2 knots. We prefer that to motoring. I can't give an exact windspeed because I don't trust the instruments to that level, but being blown along 'dead down wind' we'd be going very slowly.
The vagueness is made worse by the fact it's often better not to sail in a straight line, I head up to build speed then bear off as the apparent moves forward.
Repeat on each wave sometimes!

Maybe IP would be able to produce polar diagrams for your boat with those sails?
But be sure they account for things like the fixed prop if you have one.

 

[Laminar Flow]

Hi Rotax,
I guess, looking at the numbers for your boat on Sailboat data, that the largest sail you will be looking at would be around 1000 sqft.
Together with your main you would then be able to set somewhere in the region of 1300 -1400 sqft from a close reach on downward.

On a reach 1sqft of sail develops in: a F3 - 0.015HP, in a F4 - 0.02HP, in a F5 - 0.04HP and in a F6 0.07HP.

The next step is to calculate resistance of your boat. Resistance in displacement craft is directly proportional to displacement and speed. Since you are looking at enhancing light weather performance I would suggest looking at a speed length ratio of 0.9, which, incidentally, is the average speed for boats under sail and the point just before form resistance rises exponentially. For your boat with a DWL of 39.75' that is 5.75 kts.

Using the graph in Kinney, Elements of Yacht Design, pg 85, you get a factor of 11 for a relative speed of 0.9.
The formula is: tons of displacement x the factor (11) = resistance.

Next is to calculate E.H.P or effective HP required to drive your boat at a certain speed.
The formula is: resistance x speed x 0.003.

Now you can correlate the power your rig can develop with the speed you can or want to obtain. You can also establish a relationship of your engine output at various RPM versus your speed, bearing in mind that only about 50% of your actual shaft horse power is converted into propulsion.

Feel free to PM me if you would like further info.

You can establish your own polar diagrams with the above info by calculating VGM using boat speed and the sine function of your relative angles to the wind.

 

[flaming]

I am waiting for a reply from the factory about sail dimensions. While reading about code zero/reachers I became confused as some suggest they are for use 30 to 90 degrees before the mast and other say they can be used for downwind sailing.

Perhaps they can do both?

There are code zeros, and there are code zeros, and there are reaching sails.... If you get my meaning.

The shape and size of any sail is a compromise. If you want it to be good close to the wind it needs to be comparatively smaller and flatter than one that is good for off the wind. It's perfectly possible to go to a sailmaker and say "I want a sail to power my boat up in 8 knots of wind on a TWA of 60 degrees, and they would build you a sail that would do exactly that, and it would revolutionise sailing in 8 knots of wind at 60 degrees for you. But as soon as you start broadening the window you want to use the sail in, such as saying 6-12 knots and 60-100 TWA, then the sailmaker has to compromise, as obviously the perfect sail in 6 knots at 100 is quite different from the sail you want at 12 knots at 60. Start asking one sail to cover 60-150 TWA and you're really asking too much.

So the first step is to identify the actual hole in your polars you're trying to plug. And if it's really just "light winds" then ask yourself how many sails you want to buy. If just one, then look at if you're really looking for a downwind sail, or a reaching sail. Also bearing in mind that very full "downwind" assys aren't big fans of furling.
My advise would be to go for the biggest, fullest sail you can get to furl. That should work OKish in very light winds at reasonably hot angles - say up to about 80TWA in less than 8 knots, but continue to work well in medium winds sailing much more off the wind. It would mean you would still probably be a bit underpowered in say 9-10 knots on a reach where you couldn't hold the sail, but I think that's probably a good compromise.

 

[Laminar Flow]

There are code zeros, and there are code zeros, and there are reaching sails.... If you get my meaning.

The shape and size of any sail is a compromise. If you want it to be good close to the wind it needs to be comparatively smaller and flatter than one that is good for off the wind. It's perfectly possible to go to a sailmaker and say "I want a sail to power my boat up in 8 knots of wind on a TWA of 60 degrees, and they would build you a sail that would do exactly that, and it would revolutionise sailing in 8 knots of wind at 60 degrees for you. But as soon as you start broadening the window you want to use the sail in, such as saying 6-12 knots and 60-100 TWA, then the sailmaker has to compromise, as obviously the perfect sail in 6 knots at 100 is quite different from the sail you want at 12 knots at 60. Start asking one sail to cover 60-150 TWA and you're really asking too much.

So the first step is to identify the actual hole in your polars you're trying to plug. And if it's really just "light winds" then ask yourself how many sails you want to buy. If just one, then look at if you're really looking for a downwind sail, or a reaching sail. Also bearing in mind that very full "downwind" assys aren't big fans of furling.
My advise would be to go for the biggest, fullest sail you can get to furl. That should work OKish in very light winds at reasonably hot angles - say up to about 80TWA in less than 8 knots, but continue to work well in medium winds sailing much more off the wind. It would mean you would still probably be a bit underpowered in say 9-10 knots on a reach where you couldn't hold the sail, but I think that's probably a good compromise.

In regards to performance in racing terms that is all correct, but in the context of cruising convenience on an underigged 17 ton motorsailer I am less than certain that excellence in such narrow performance windows is what the OP is after. For the overriding benefit of keeping things simple and the old girl moving in anything less than 10 kts and within some broader range of bearings, I'm quite sure he will be willing to compromise on some points. With an effective SA/D ratio of 10.6, anything that increases SA in these conditions will be profitable, regardless of the finer points and in this I agree: go as big as possible and as is safe to furl.

 

[rotrax]

Thanks guys, the rigger is installing the forestay and furler Thursday.

Once the exact dmension of the luff are clear our reccomended sailmaker, PS in Lymington can start on the sail.

Final talks with him re material weight, shape and furling.

Looks like we shall go for around 1000 sq feet.

This forum really is the place for good advice and technical know how. ?

 

[flaming]

In regards to performance in racing terms that is all correct, but in the context of cruising convenience on an underigged 17 ton motorsailer I am less than certain that excellence in such narrow performance windows is what the OP is after. For the overriding benefit of keeping things simple and the old girl moving in anything less than 10 kts and within some broader range of bearings, I'm quite sure he will be willing to compromise on some points. With an effective SA/D ratio of 10.6, anything that increases SA in these conditions will be profitable, regardless of the finer points and in this I agree: go as big as possible and as is safe to furl.

Yes, that was exactly my point.... Sorry if I wasn't clear.

 

[ashtead]

Be interested to hear which sail cloth you opt for -nylite by contender sailcloth is the one I’m looking at currently.

 

[dunedin]

Be interested to hear which sail cloth you opt for -nylite by contender sailcloth is the one I’m looking at currently.

Surely it depends a lot on whether the sail is to be kept hoisted and furled, in which case needs UV strip - and hence into lightweight genoa sailcloth territory, as opposed to a code type asymmetric, which would be much lighter material.
Having fitted a forestay, very much into conventional genoa territory.

 

[ashtead]

1000 sqfoot is a large Genoa surely ?

 

[Laminar Flow]

1000 sqfoot is a large Genoa surely ?

Nowadays, perhaps, when a genny is rarely larger than 130%, but frequently less to make roller reefing feasible as opposed to simply furling. 150% used to be common, 180% even. Besides, Rotrax boat 's a big girl.

 

[rotrax]

Riggers attended yesterday, Facnor and forestay plus halyard diverter fitted . OE fitting at masthead was used, the lower connected to my fabricated fitting copied from the design of the OE Jib forestay lower fitting. I fitted that the previous day. I had to buy an overlength drill bit to get through the 6 inch thick Bowsprit. Butyl tape - colour matched - was used as a sealer.

I have a new Lewmar 45 ST Evo winch, a double and single clutch, sheet blocks, furling line and turning line blocks for Starboard side to power winch, plus sheets.

Already sourced some teak for the required positioning of the clutches and turning blocks. I have left over from my Motorbike Racing days some suitable high quality 12mm duralumin plate for making the under deck hard points for mounting this hardware. Fortunatly they have reasonable access from inside.

Discussion with PS at Lymington re cloth/size/shape and UV strip Monday.

Thanks for your help, watch this space. ?