Sailboat Calculator

[Terry]

I found this interesting sail calculator on another site:
http://www.image-ination.com/sailcalc.html
The various models of MacGregors are listed so I decided to do a comparison. My only other real life comparison that I have any experience on was a 26' Thunderbird (an old classic sailboat) so I used it as a measuring stick. Surprisingly, quite a few similiarities showed up even though they are entirely different species. You can try a comparison to any model you wish but I used the Thunderbird because I know it to be very similar in dimensions. Of course in a race I am sure the Thunderbird would leave the Mac in its wake but it is still interesting to see how similar the dimensions are.

[Bransher]

Thanks, this is an interesting tool to have.
Now when someone passes me, I will know it is my technique and not the boat at fault.

[Rick Westlake]

Ran their numbers for a MacGregor 26X - very interesting! (I cleaned it up a little, and added the explanations for everything the program explains.) They have other MacGregors listed as well - or you can input your own figures for LOA, LWL, beam, displacement and sail area.

SailCalculator.com Report - MacGregor 26X
Length Overall = 25.833
Length at Waterline = 23
Beam = 7.833
Displacement = 4225
Sail Area = 281

Displacement To LWL = 155
A medium value would be 200. 300 would be high (Heavy Cruising Boat) and 100 would be low (Ultra Light Displacement-ULDB). Boats with low numbers are probably uncomfortable and difficult to sail.

Hull Speed = 6.43
This is the maximum speed of a displacement hull. Some racers and lighter boats are able to achieve greater speed by lifting over the bow wave and riding on top of the water,that is, planing.

Sail Area To Displacement = 17.2
The sail area is the total of the main sail and the area of the front triangle. I cannot be sure that this datum was entered correctly for each listed boat. A racing boat typically has large sail area and low displacement. A number less than 13 probably indicates that the boat is a motorsailer. High performance boats would be around 18 or higher.

LWL To Beam = 2.94
A medium value would be 2.7. 3.0 would be high and 2.3 would be low.

Motion Comfort = 17.52
Range will be from 5 to 60+ with a Whitby 42 at the mid 30's. The higher the number the more comfort in a sea. This figure of merit was developed by the Yacht designer Ted Brewer and is meant to compare the motion comfort of boats of similar size and types.

Capsize Ratio = 1.94
A value less than 2 is considered to be relatively good; the boat should be relatively safe in bad conditions. The higher the number above 2 the more vulnerable the boat. This is just a rough figure of merit and controversial as to its use.

Pounds per Inch Immersion = 644
The weight required to sink the yacht one inch. If the boat is in fresh water multiply the result by 0.975. If you know the beam at the waterline (BWL) multiply the result by BWL/Beam.

Not really any great surprises here - the light weight and water ballast give us a high SA/D ratio at the expense of sea-kindly motion. On the other hand, ours are good light-wind vessels; I can enjoy myself under sail while heavier-displacement cruisers are resorting to the "iron jib". And the "capsize ratio" suggests that we are still "relatively safe in bad conditions" ... although I'm not eager to press that.

Check out your Mac ... you will at least be amused. I'd be interested in seeing Highlander's figures with the bowsprit.

- Rick

[Highlander]

Ran their numbers for a MacGregor 26X - very interesting! (I cleaned it up a little, and added the explanations for everything the program explains.) They have other MacGregors listed as well - or you can input your own figures for LOA, LWL, beam, displacement and sail area.

SailCalculator.com Report - MacGregor 26X
Length Overall = 25.833
Length at Waterline = 23 ( 23.17)Highander
Beam = 7.833
Displacement = 4225 (3950)
Sail Area = 281 ( 506)

Displacement To LWL = 155 (142)
A medium value would be 200. 300 would be high (Heavy Cruising Boat) and 100 would be low (Ultra Light Displacement-ULDB). Boats with low numbers are probably uncomfortable and difficult to sail.

Hull Speed = 6.43 (6.45)
This is the maximum speed of a displacement hull. Some racers and lighter boats are able to achieve greater speed by lifting over the bow wave and riding on top of the water,that is, planing.

Sail Area To Displacement = 17.2 (32.4)
The sail area is the total of the main sail and the area of the front triangle. I cannot be sure that this datum was entered correctly for each listed boat. A racing boat typically has large sail area and low displacement. A number less than 13 probably indicates that the boat is a motorsailer. High performance boats would be around 18 or higher.

LWL To Beam = 2.94 (2.96)
A medium value would be 2.7. 3.0 would be high and 2.3 would be low.

Motion Comfort = 17.52 (16.31)
Range will be from 5 to 60+ with a Whitby 42 at the mid 30's. The higher the number the more comfort in a sea. This figure of merit was developed by the Yacht designer Ted Brewer and is meant to compare the motion comfort of boats of similar size and types.

Capsize Ratio = 1.94 (1.98)
A value less than 2 is considered to be relatively good; the boat should be relatively safe in bad conditions. The higher the number above 2 the more vulnerable the boat. This is just a rough figure of merit and controversial as to its use.

Pounds per Inch Immersion = 644 (648)
The weight required to sink the yacht one inch. If the boat is in fresh water multiply the result by 0.975. If you know the beam at the waterline (BWL) multiply the result by BWL/Beam.

Not really any great surprises here - the light weight and water ballast give us a high SA/D ratio at the expense of sea-kindly motion. On the other hand, ours are good light-wind vessels; I can enjoy myself under sail while heavier-displacement cruisers are resorting to the "iron jib". And the "capsize ratio" suggests that we are still "relatively safe in bad conditions" ... although I'm not eager to press that.

Check out your Mac ... you will at least be amused. I'd be interested in seeing Highlander's figures with the bowsprit.

- Rick

Here you are I put mine in the brkts beside your X Stats as a comparison J

[mikelinmon]

Hi folks,

Not to debunk anyone else and their calculator; bunk! One of the most important elements to capsize "ratio" was not in the formula. Where is the freeboard in their formula? Our boat has extra capsize protection from the wide top of the deck. Picture our boat pulled all the way over and then forced even further, such as a rollover from a big boat pushing us down. The cabin top is enough to right the boat, not even counting the hull freeboard. Also, the mast has floatation in it with the 30' or more lever arm. Betting once freeboard is added to the formula in its proper place and mast floatation is added in, the 26M is tops. Period. Compare us to a J24 (a wonderful boat and I really like them); they are way stiffer at sailing speeds/wind and all. They are happy falling right over if pushed hard enough and will stay upside down for a short while till they sink. But, the J will come out better in this formula. Just need to add in the full story to the formula!
Mike Inmon

But I do like the idea of a way to compare, just work all of the parameters into the mix.

[drams_1999]

Here is the same info for the Mac M

Length Overall = 25.833
Length at Waterline = 23.17
Beam = 7.833
Displacement = 3950
Sail Area = 300

Displacement To LWL = 142
A medium value would be 200. 300 would be high (Heavy Cruising Boat) and 100 would be low (Ultra Light Displacement-ULDB). Boats with low numbers are probably uncomfortable and difficult to sail.

Hull Speed = 6.45
This is the maximum speed of a displacement hull. Some racers and lighter boats are able to achieve greater speed by lifting over the bow wave and riding on top of the water,that is, planing.

Sail Area To Displacement = 19.21
The sail area is the total of the main sail and the area of the front triangle. I cannot be sure that this datum was entered correctly for each listed boat. A racing boat typically has large sail area and low displacement. A number less than 13 probably indicates that the boat is a motorsailer. High performance boats would be around 18 or higher.

LWL To Beam = 2.96
A medium value would be 2.7. 3.0 would be high and 2.3 would be low.

Motion Comfort = 16.31
Range will be from 5 to 60+ with a Whitby 42 at the mid 30's. The higher the number the more comfort in a sea. This figure of merit was developed by the Yacht designer Ted Brewer and is meant to compare the motion comfort of boats of similar size and types.

Capsize Ratio = 1.98
A value less than 2 is considered to be relatively good; the boat should be relatively safe in bad conditions. The higher the number above 2 the more vulnerable the boat. This is just a rough figure of merit and controversial as to its use.

Pounds per Inch Immersion = 648
The weight required to sink the yacht one inch. If the boat is in fresh water multiply the result by 0.975. If you know the beam at the waterline (BWL) multiply the result by BWL/Beam.

So....where do they account for the blue hull vs. white hull??

[Trouts Dream]

Blue absorbs light more than white thus adding to the overall weight and slowing the boat down albiet marginally.

[Rick Westlake]

Here you are I put mine in the brkts beside your X Stats as a comparison J
Sail Area = 281 ( 506)

Sail Area To Displacement = 17.2 (32.4)
The sail area is the total of the main sail and the area of the front triangle. I cannot be sure that this datum was entered correctly for each listed boat. A racing boat typically has large sail area and low displacement. A number less than 13 probably indicates that the boat is a motorsailer. High performance boats would be around 18 or higher.

I didn't realize your bowsprit was that long!

[Highlander]

Rick

remember I am cutter rigged so I can fly two head sails together at the same time
http://s844.photobucket.com/albums/ab1/ ... 010091.flv

J

[Rick Westlake]

Sorry, John. I thought "front triangle," for SailCalc, refers to the triangle between your outer forestay, your mast, and your deck - "IJ/2". Nothing I read in the Web page's directions suggested to me that you could count the space within your inner forestay twice - any more than they'd have us use the whole area of a 150% genoa as the "front triangle".

[Currie]

...Not to debunk anyone else and their calculator; bunk! One of the most important elements to capsize "ratio" was not in the formula. Where is the freeboard in their formula? Our boat has extra capsize protection from the wide top of the deck. Picture our boat pulled all the way over and then forced even further, such as a rollover from a big boat pushing us down. The cabin top is enough to right the boat, not even counting the hull freeboard. Also, the mast has floatation in it with the 30' or more lever arm. Betting once freeboard is added to the formula in its proper place and mast floatation is added in, the 26M is tops. Period. ... Mike Inmon

Hi Mike,

Makes perfect sense to me - and I agree. If I may ask, why doesn't the factory just post the stability plots like the other manufacturers do? It should be very favorable - and it should put an end to a lot of speculation.

Cheers,

~Bob

[mikelinmon]

We really need to do something like that. Our ultimate stability is very good compared to allmost anyone. Roger's computer can do that very thing, now just to take time to do it. I'd really rather go sailing but will do it anyway! Soon, maybe.
Mike Inmon

[Currie]

Sounds great, Mike

BTW - The high-winds video has gone a long way, IMO, to open some minds - not that I hope to see many Mac's doing the same. I've had to send the link to a couple of friends already, in response to "concerns" about my water-ballasted vessel. They were pretty impressed. Heck, I was impressed how stable it is in 12+ foot waves. Which begs a question - did you ever get a knock-down out of that trip? No shame here, given the conditions - be honest

Cheers,
~Bob

[bubba]

Mike: I noticed I think the Mac M in the high wind vidio You were not using a BOOM VANG and that let you dump extra wind out of the sails. Is that what happened ???

[Currie]

Mike: I noticed I think the Mac M in the high wind vidio You were not using a BOOM VANG and that let you dump extra wind out of the sails. Is that what happened ???

Hmm, Im confused. I wouldn't use a boom-vang to dump, but rather, I'd pull the traveller to windward and release the boom-vang completely. A boom-vang reduces twist - the opposite of dumping. Did I misunderstand?

~Bob

On Edit: Yarrr!! - I'm talking about "spilling", not "dumping". I think I see what you're saying - vang it in hard and dump the mainsheet on the puffs - (maybe?)