boat speed

[lateron]

This may have been posted before but as a relatively new owner of a SO 32 2004 1.5 keel could I ask for opinions on:

1. When I first got the boat my log read let's say 5.5 k when SOG across the tide was 7k. I recalibrated my log to almost match the SOG and now frequently see 7k + on the log in a decent breeze, max so far 8k. Is that about what you would expect from a SO32?

2. My boat is faster by at least half a knot on one tack than the other . Why? Can I do anything about it, my last boat a Hunter Ranger 265 was the same, is it the impellor position or is there some scientific reason?

Welcome your comments......... cheers Ron

[Don Reaves]

See the thread titled "Performance difference on starboard and port tack" in the Performance section for a discussion of issues that might cause your problems.

[MartyB]

clicky

The post Don mentioned, I clickied above, has a number of thoughts on the how and why.

marty

[tedp]

Hello Ron

Max speed I read on the GPS under sail up to now was about 6.9 knots (on a lake devoid of tidal streams) which concurs with the theoretical hull speed for the SO32.

The issue of differing speeds on the port and startboard tack was brought up the thread "Sun Fast 26 Rig tuning" - jeanneau.proboards.com/index.cgi?board=per&action=display&thread=1419 (only a few down from the present one). I own a SO32 and I have also noticed about half a knot difference in speed reading on the log. Checking against a GPS shows that the boat sails as fast on one tack as on the other, so the cause can only be the log. The paddlewheel is off centre on my boat, it might be similar in yours.

So there should be nothing wrong with your mast, or the shrouds, or anything. It's due to someone not thinking when he fitted the log transducer off-centre, side by side with the depth sounder. The flow around the impeller on one tack is slightly different from the other.

I calibrated my log against the GPS, running about 5 knots under engine in flat water, and if I check there will be differences along the entire speed range due to the limitations of the mechanical log instrument. I never trust them myself, they're only useful for coarse reading.

Hope that eases your mind!

best wishes

Ted

[lateron]

thanks guys......sorry to raise an old chestnut. I'm favouring the paddlewheel reasons although I may check the rig also.
So tedp or anyone else would you say that the GPS is always the more accurate measure of boatspeed
[ allowing for the tide that is?]
Cheers Ron

[tedp]

An old chestnut? No, not at all. Please feel free to ask.

Yes, the GPS is the more accurate instrument. It reads satellite fixes continually with an accuracy of about 10 to 15 yards, so if the samples are added up and compared over a number of seconds you have a very accurate reading. The speed given to you is calculated by the device and corrected for any signal errors. But it will give you the speed over the ground, not through the water.

Any sensor operating in the transition zone of turbulent water close to the hull of a vessel is bound to be inaccurate and will only give you a rough estimate. If you don't have anything else to go on, a log instrument, compass and tide prediction are good for a short period of dead reckoning, but as soon as possible you have to verify your position by an external fix. Any professional sailor will tell you that.

Best wishes, Ted

[corksailor]

Raced the So 35 against an So32 with deep keel last weekend and lost on the water.Sails and trim matter more.The 32 was faster downwind (No kites).On both boats we noticed a difference in speed on port and starboard tacks upwind.Time to pay the rigger again!

[davideso37]

Difference in speed on port or starboard tack can be caused by wave and tide conditions and distribution of gear in the yacht. If both yachts have a similar difference between port and starboard then wave and tide conditions are to be suspected. As others have noted the location of the paddle wheel sensor will cause different readings on port and starboard. Yes the GPS is more accurate but only with respect to speed over the ground, not speed through the water. Find some flat water with no tide, check that the gear on board is evenly distributed from side to side and then check the GPS speed on the two tacks.
Regards
David

[dublin]

I attended a lecture some year ago given by the sailmaker DES McWilliams - also very good racer including surviving the fasten storm in 1979. He explained that due to the coriolas effect, friction of the water altering wind direction lower down etc, the reading of the wind instrument on the masthead is about 15degrees different from ypthe acyptual wind at sea level. As only a small proportion of the sail power is at the masthead the masthead reading is not showing the same wind angle as say at the middle of the sail. As a result the real wnd in the sails is up to +15 degrees on one tack and -15degrees on the other tack from the reading shown by the masthead instruments. This means that although the instruments are telling you that you are at the same angle to the wind on each tack you are not actually at the same angle.

I think I got that right !!

On a less technical level on sone Jeanneaus all of the machinery is put on the same side of the boat and a compensating weight is meant to be on the other side. This is sometimes left out by "mistake". I had this problem with a 2002 so32

[tedp]

As I mentioned in an earlier post, my boat if measured on the GPS in a lake devoid of tidal streams does the same speed on both tacks. At the same time the paddle wheel log shows a marked difference on both tacks.

If the boat lies on an even keel in flat water, the weight is distributed evenly and the centre of gravity is in the centre line of the boat. This means that a given heeling moment whether to starboard or to port will always result in the same amount of heel.

If you sail by the set of your sails on both tacks and trim them the same (i.e. by just preventing back pressure on the forward edge of the sail and keeping the telltales a-stream) instead of relying on the wind instrument, and the boat's performance on the GPS is identical on both tacks, the only thing that reads wrong is the log. It has nothing to do with your rigging, so save yourself the cost of having it seen to. As I explained, a log is a very inaccurate instrument compared to the GPS and it should never be trusted on its own.

If you know the standard error in log reading on each tack however, in tidal waters it is possible to estimate the amount of current you're experiencing by comparing the log reading to the GPS (which gives the speed over the ground). So if the log normally reads half a knot more than the GPS on the starboard tack, and you see the GPS reading drop two knots below the log reading, you have a knot and a half of current against you. I hope you are still with me....?

[lateron]

Hi guys...........I think my 2004 SO32 is one of those on which the compensating weight has been left out as it has a list to starboard. Would putting things on an even keel improve performance and how might one safely go about this? I've already put my extra anchor to port.There isn't room for large objects. Has anyone out there done this correction?

Cheers Ron

[MalcolmP]

Apr 1, 2011 16:03:39 GMT lateron said:

Hi guys...........I think my 2004 SO32 is one of those on which the compensating weight has been left out as it has a list to starboard. Would putting things on an even keel improve performance and how might one safely go about this? I've already put my extra anchor to port.There isn't room for large objects. Has anyone out there done this correction?

Cheers Ron

Hi Ron

On the SO34.2 a large block of lead was used

You might be able to do something similar

Malcolm

[lateron]

OMG !!...........that looks a pretty serious piece of lead! Maybe I'll carry on listing. I could stuff the wife in there! But then she wouldn't cook my breakfast.

Bye Ron

[tedp]

In my SO32 I think there is a large block of something behind the back rest of the port side settee. We came across it when installing the air ducts for the heating system. I thought it was concrete but I haven't yet checked. Probably that is meant to get the boat on an even keel.

Have you thought of bricks stacked behind the settee and fixed with polyurethane foam? That might make a considerable weight.

[MalcolmP]

Apr 1, 2011 17:13:01 GMT lateron said:

OMG !!...........that looks a pretty serious piece of lead! Maybe I'll carry on listing. I could stuff the wife in there! But then she wouldn't cook my breakfast.

Bye Ron

Ron

Hope your wife doesn't read that, otherwise it will be you that is the ballast

cheers

Malcolm

[MartyB]

They put that piece of lead that high because why!?!?!?!? I would prefer to see something like that a bit lower in the hull. Then again, my Arcadia lists a bit to one side too, as do others I know of......hmmmmmm............

[lateron]

I agree about the height of the lead. I was thinking maybe I might use some old anchor chain wrapped in polythene and put in bottom of a locker.
Or as I said before just grin and bear it.

Regards Ron

[tean]

Our Sun Light 30 has the fuel tank (10gallons) beneath the chart table to starbord and two 20 gallon water tanks, one under the starbord saloon berth and one under the port saloon berth. When all are full, she lists to starbord. There is no lead weight.

We use up the water in the starbord tank first and the list decreases and eventually she lists to port, then we use up the port tank and she gradually comes upright until, when both are empty she lists to starbord again, ready to be refilled.

We could with more careful switching between tanks, keep listing down to a minimum once we had used about 10 gallons from the starbord tank. I guess we could fit a transfer pump and attempt to keep her on an even keel by transferring water as required. Maybe an automatic levelling system could be devised with a list sensor?

[flightdeck]

Lead..50kg of it, it's placed where it is, port side, to help leveling her up.....the yacht that is not the wife. It's a sad way of fixing a design fault, but when diesel tank, cockpit locker, galley is all on the starboard side and you only have the head to counter balance with, solution is 50kg of lead on the port side, looks like that has been worked out better on the 33i, mind you we just carry our junk (sails, crew gear) on the port side when racing.
As always with a Jeanneau it's a compromise.

[tedp]

Apr 2, 2011 16:44:33 GMT lateron said:

I agree about the height of the lead. I was thinking maybe I might use some old anchor chain wrapped in polythene and put in bottom of a locker.
Or as I said before just grin and bear it....

The higher up the piece of lead is, the further from the centreline it will be due to the round hull section. So I think it has been put in the best possible place as what matters most is the leverage it will exert.

Under the seats it will be less effective than where it is now. Putting 50kgs of weight 1 metre or 50cms above the centre of weight won't make much difference in a 4.5 ton deadweight boat with all that ballast hanging underneath. If you stand on the cabin roof yourself, you will reduce stability much more than that piece of lead sitting under the gangway.

I think they made the best compromise they could given the fact they put in such a comfortable and wide stern berth and having to stow a lot of gear to starboard.