What boatspeed should I expect, as a percentage of True wind?

[smj]

Originally Posted by arsenelupiga

see his original post . 10 kn wind at 75 app boat speed 7.5 kn. We can do 6.5 kn with gennaker.

I’m guessing once he gets his gennaker he will be sailing close to windspeed.

[GRIT]

Originally Posted by smj

I’m guessing once he gets his gennaker he will be sailing close to windspeed.

That's the plan. Those speeds were with the mainsail and 101% jib. The Code 0 will add about 60m2 of sail area over that combination.

Cheers.
Paul.

[GRIT]

Originally Posted by jmh2002

I would suggest yes, if the data is thereafter being used for important functions (eg: as mentioned, autopilot) rather than just a cursory glance and a general "oh, it's blowing 20ish knots".

But I also don't think it's essential to buy one of the (very expensive) factory 'wands'. If there is sufficient cable length why not just run it up on an extension tube of one's own design (no different to how it runs up inside the mast) ?

Although I do admit that the size of the plug on the end of the end of the cable could proof troublesome.

But there are also various wireless options to consider these days too.

I've read, but not tried, that B&G has offsets you can plug into the autopilot computer to account for updraft at certain angles. It requires you know the actual speed, but I think by changing your heading a few times, that can be sussed out.

Having a fractional rig, I'd assume our speeds would be fairly accurate going into the wind, and not so much off the wind. Going back and forth a few times should get us close with the offsets. Though I know that's not a replacement for getting the wand out of the way of the updraft.
The wand was quite a lot of money, and I wasn't convinced of it's value, so we opted out, for now.

Cheers.
Paul.

[jmh2002]

Yes, the B&Gs do normally have that feature, and it helps, but as you said it varies based on heading, wind speed, and sail combination.

In the past on one particular boat (a cruiser/racer mono) we had B&Gs and then upgraded to the latest top of line race versions at the time.

Because we raced the boat we did a lot of work together a friend of mine, who was a B&G tech, calibrating all the electronics, speed, wind, etc, as well as tack to tack, and upwind and downwind.

It's quite a process to get it right but the results were worth it. This also paid off from a cruising point of view when were using the autopilot to steer to apparent wind angle - in fact it steered in this mode almost all the way across the Atlantic from Antigua to the Azores, even with the spinnaker up, and did an amzing job, really helping to keep the boatspeed average up.

The other factor to consider, although it may be less so on a cruising boat (or more so because of being short handed?) is if you have a free flying sail get a bit a bit out of control, it can rise up and sometimes damage the wind gear - being higher up (and normally forward too) on a wand helps prevent that.

I hope that's some extra info for you

[Tupaia]

Mine has a short stand off. The problem used to be the old style tri-colour/anchor lights 300mm or so so that would disturb the flow downwind, even with an extra long wand, but with new LED masthead light 40mm the anemometer sits in clean air.

[GRIT]

Thanks guys, for your B&G input. We just had a great sail from Deltaville to Virginia beach, and during this sail, I managed to do some testing. It's fairly obvious I'm showing inaccurate windspeeds when the wind's aft of say 110 degrees or so.

I can see how jmh2002 had to do lots of work to get the settings right, and I think it's going to be worth it to get that sensor out of the mainsail wash. We'll get the extension.

We won't have issues with the spinnaker touching the sensor, as even the spinnaker is fractionally rigged. It sits at 17m above deck, whereas the masthead is 19.5m above deck.

It's a steep learning curve. Made easier by helpful posts, as I've been getting on this thread.

Thank you all for your contributions so far.

Cheers.
Paul.

https://www.youtube.com/watch?v=HY6miDPbmEU

[JustMurph]

GRIT: She sounds like an awesome boat! Who was responsible for the design?

I'm short on time today so haven't read all responses, but here are a few data points on my Mumby 48 that I can recall off the top of my head. So she's 14.4 x 7.4m, 7t light ship, probably sitting at closer to 9 or 10t in full live aboard cruising mode, dagger boards, 0.5m draft, kick up rudders, 76m main, 48m genoa, 105m code D and 145m aysm. The main is a bit blown out and the shape isn't great any more. The others are ok.

In 15 knots TWS, we'll be hard on the wind at ~33º and 8.5knots (56%). It's very happy here. In 8 knots TWS we'll do about 6.5 knots (80%).

I don't recall any good light wind data points for a reach, but a few days ago we sat on a sustained 11.5 knots in ~22 knots TWS with full main and full genoa for about half an hr.

DDW wing on wing, we'll sail just below 50%. Get the spin up and crack off a bit and we'll average average maybe 75% with a bit of sea state, closer to wind speed with smooth water, and can exceed wind speed if I come up a bit further.

[GRIT]

Thanks for that response JustMurph. Those are very similar numbers to what I'm seeing.

We don't yet have any light wind sails, and our jib is only 100%, with no overlap. We don't have an overlapping genoa, but have ordered a code 0, and a prodder, which should help quite a lot.

I'm encouraged by your sailing numbers, as our boats are very similar in dimensions and mass. Loa 15m, Beam 7.6m, draft .6m with boards and rudders raised, and the props folded. Draft with boards down is 2.2m. Hull beam to length ratio is 12.5:1. Displacement 7.5 Tonnes light(ish), and 8.5 Tonnes when hauled out last month. Main 75m2, jib 37m2, Code 0 is expected to be 100m2.

We plan to use the code 0 for a while, then decide what to get next: Either a Screecher for upwind in light airs, or a spinnaker for going the other way. We'll probably get the spinnaker, as I'm happier going downwind than up!

The design was originally a Kurt Hughes 45, which Kurt modified to our specs. We had him lengthen the hulls, shorten the bridgedeck, delete 2 berths, add a carbon composite bow beam, and some other modifications that are too boring to read here. We also added the forward cockpit, inside steering, and internal layout, to our own design, as Kurt assures us that the house isn't structural to the boat.

Thanks again. Your post was very helpful.

Cheers.
Paul.

PS. We're a big fan of the Mumby's, and aluminum boats in general.

[JustMurph]

No problem, happy to help. Grit sounds like a pretty damn awesome boat!

For what it's worth, I agree going a code 0 or more of a reaching or upwind light air flying sail is the way to go. The previous owner of my boat bought the code D because he didn't like using the spinnaker. I don't mind using the spin, so if anything I'd rather have a light air sail that can point a bit higher.

In light air with the code D, sailing to a destination downwind, I find I need run too large of an angle to get decent speed, so my VMG doesn't really end up all that much better. It does work well from a broad reach to a reach.....but so would a Code 0. For running, in a faster boat like yours, you can run the spinnaker a fair way up the wind range.

[GRIT]

Thanks JustMurph, for the compliment.

It looks like your boat is just as fast as we hope to be, so I'm sure our sail choices will be similar.

I'm happy using a symmetrical spinnaker (on a cat), but will also look into Asym's, as that seems to be the way of cats these days. But for this season, we'll see what the code 0 will do for us. I'm excited to try it out.

A sister ship used to run 3 different sized symmetrical spinnakers, for his tradewind sailing. That was his whole "non white sail" wardrobe, and he did fairly well with those, running 175 miles per day (on the rum line) and often over 200 miles per day through the water.

I've got a lot of learning to do, but I'm enjoying it.


Cheers.
Paul.

[jmh2002]

Good stuff!

[Chotu]

This is great!

Wind speed!

Congratulations on everything. Goals attained!

[barnakiel]

Originally Posted by JustMurph

No problem, happy to help. Grit sounds like a pretty damn awesome boat!

For what it's worth, I agree going a code 0 or more of a reaching or upwind light air flying sail is the way to go. The previous owner of my boat bought the code D because he didn't like using the spinnaker. I don't mind using the spin, so if anything I'd rather have a light air sail that can point a bit higher.

In light air with the code D, sailing to a destination downwind, I find I need run too large of an angle to get decent speed, so my VMG doesn't really end up all that much better. It does work well from a broad reach to a reach.....but so would a Code 0. For running, in a faster boat like yours, you can run the spinnaker a fair way up the wind range.

Yep.


Other than racing - where every smallest difference may be a win - cruising cats do best ddw under spinnakers. Most people do not understand how easy it is to fly a symmetrical kite on a cat.


My friends sailing a L40 have just arrived in the Caribbean having sailed nearly pure ddw track and never once sailing less than 140 dmg miles. The only time they dropped the kite was to shorten the halyard.



Cheers,
b.

[JustMurph]

Originally Posted by barnakiel

Yep.


Other than racing - where every smallest difference may be a win - cruising cats do best ddw under spinnakers. Most people do not understand how easy it is to fly a symmetrical kite on a cat.


My friends sailing a L40 have just arrived in the Caribbean having sailed nearly pure ddw track and never once sailing less than 140 dmg miles. The only time they dropped the kite was to shorten the halyard.



Cheers,
b.

I don’t know that I entirely agree with that, but I might just get a chance to test it tomorrow with what looks like it will be a light DDW run home in the arvo.

My understanding is that on fast cats like these, you are better off running angles in lighter winds and DDW as the wind speeds come up. In my above example with the Code D, I think my mistake was that the wind was light enough that I should have been running the spinnaker, in which case I could have run a lot deeper, with a far better VMG. I chose to stick with the code D as it was just me and one very green friend.....and we had lots of time.

[Dave_S]

Originally Posted by JustMurph

I don’t know that I entirely agree with that, but I might just get a chance to test it tomorrow with what looks like it will be a light DDW run home in the arvo.

My understanding is that on fast cats like these, you are better off running angles in lighter winds and DDW as the wind speeds come up. In my above example with the Code D, I think my mistake was that the wind was light enough that I should have been running the spinnaker, in which case I could have run a lot deeper, with a far better VMG. I chose to stick with the code D as it was just me and one very green friend.....and we had lots of time.

I'll be surprised if you can improve VMG direct down wind by gybing but your destination must be DDW, not 20° off. Even without spinnaker, just comparing gybing to wing on wing I think wing on wing will be faster. It won't feel like it though.