Boat speed under sail?

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james.brine
james.brine's picture
Boat speed under sail?

Hi guys. Sorry it's been so long. Hope you are back in the water despite this horrible virus.

I know the subject of speed of MacGregors has been flogged to death regarding power but my question is regarding sailing speeds:

As some of you will know we had a bit of an adventure last year and covered a lot of ground/water around the south coast. Needless to say, making good ground to the next safe harbour became important to our progress. I became somewhat frustrated with my boat speed at times. Now, I sailed nearly 600NM last year but that doesn't mean I'm any good at it so I'm happy to accept that my lack of go may be down to lousy technique but in my defence, all tell-tales we're doing as they should and sail shapes looked fine. The rig on my boat is not entirely standard and this is also under scrutiny at the moment. Before I spend a fortune and a great deal of time attempting to squeeze an extra knot out of the old girl, I want to know I'm not wasting my time. I've never really heard anyone complain about boat speed under sail so my question is this:

In say, 10-12 mph wind with full sail (I have a jib on the pointy end) what speed would other Mac owners expect to achieve on a braid reach, beam and close hauled?

Thanks in advance,

Jamie

james.brine
james.brine's picture
C'mon, someone must still

C'mon, someone must still sail their Mac?

mike.clarke
Depends on the sea state but

Depends on the sea state but in sheltered waters I would expect something like 6 knots on a broad reach, 4 knots close hauled and I suppose something in between for a beam reach with our 26M but this is with a slight chop which does slow a Mac down a bit with it being so light. I always found max speed of sailing in about 15knots of wind when she when really well. Above that I would reef the main and get similar speed but with more comfort. A broad reach with a reef and a good force 4 or 5 was max speed on a broad reach as she would start to surf a bit.

Hope this helps.

Mike ex Mac 26M

david.phillips
I agree with the last post. I

I agree with the last post. I unusually do 4-5 knots. Best speed under sail, 11 plus knots in a squall !

leigh.ross
leigh.ross's picture
Your're going to get 5.5-6

Your're going to get 5.5-6 knots. Your boat speed is limited by its waterline length.

The speed differences caused by sail condition, technique, skill etc are far less than they seem. If you beat me around a race course by 300 yards I'm utterly defeated. But in non racing reality , you pulled out 300 yards on me in an hour. Or in other words , maintained an average speed of 0.15knots higher than me. Not really significant in cruising life.

Leigh Ross

Crieff

0777 558-4561

1990 MacGregor 26S Ptarmigan 

1992 MacGregor 26S Pelican 

john.pompei
john.pompei's picture
Hi James,

Hi James,

As Leigh says the boat speed is primarily limited by its waterline length and the usual calculation for speed in knots and waterline in feet is 1.34 x the square root of the waterline length. So for a Mac M which I hve the waterline is 23ft so it works out at max 6.4 knots in displacement.

Mikes figures are about what you can expect provided you have everything trimmed correctly, BUT unless you are sailing on a non tidal waterway the tide will play a massive role in your speed over the ground. The other day I was beating down Stangate Creek on the Medway and SOG was almost 6Kt and I thought that when I reached the Medway I would be able to comfortably sail back to Gillingham in under 2 hours. When I reached the Medway I was on a run back up the river and virtually came to a halt, I'd sort of forgotten that I had the tide with me out of the creek and against me in the Medway that combined with being slower down wind into a 2-3 kn tide the SOG was less than a knot.

The trouble with small sailing boats is that the tide can be more than the boat speed or often a large % of its speed so as I'm sure you know after your great adventure last year working the tides is far more important than getting another knot from tweaking your rig.

I have attached the photo I took of you going down the Medway last year,

Best Regards,

John

james.brine
james.brine's picture
Right back at you John!  So

Right back at you John! So sorry it's taken me so long to get it to you. I'm a bit of a Luddite when it comes to computers and could never get stuff to upload from my idevices. Better late than never.

john.pompei
john.pompei's picture
Thanks James

Thanks James

I only use the jib as I find the Genoa difficult to manage single handed and its difficult to get the jib to gull wing

David posted about EZ cleats which may be the answer to using the Genoa singlehanded but can't find them in the UK

Regards

John

james.brine
james.brine's picture
Thanks guys,

Thanks guys,

brilliant answers as always and thanks to John for the picture (it's been my windows backdrop since you took it!)

ok, well I sometimes get close to those speeds but struggle in low winds so I think I will add a bit of sail area where I can. On a broad reach, my main shadows my foresail as it's a jib. I have gul winged it but find it difficult to maintain single handed in fluky winds. It's my intention to lengthen my forestay foil as the previous owner has fitted a replacement furler but it's very high off the deck and doesn't allow me to fly the standard sails. I own a Mac Genoa but for this reason it won't fit. I'm hoping I could still keep a Genoa flying on a broad reach and even if a can't it should give me more omph in low wind.

roly.simpson
Hard to say on the Solent as

Hard to say on the Solent as there are always tides but I often can get close to 6knt going across tide to Cowes on a reach. But there may be a vector of tide in that.

Had a great sail yesterday Yarmouth to Portsmouth in 3.5 hrs. Attached my photo but Chris Harman will have better.

leigh.ross
leigh.ross's picture
To get any meaningful speed

To get any meaningful speed increase downwind in light airs you'll need a cruising chute really.

Leigh Ross

Crieff

0777 558-4561

1990 MacGregor 26S Ptarmigan 

1992 MacGregor 26S Pelican 

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