Square root of the waterline length in feet multiplied by 1.3.

Actually is was a Swanson 28, which is a particularly stubby design. Extra sail area is only going to help you in light winds.

The sail area a yacht can fly in high winds is limited by the righting moment. So unless the boat had increased keel weight, in fact the strong wind performance would be reduced by the heavier boom and other bits and pieces added at high level.

square root of the waterline length in feet multiplied by the block co efficient. 1.3, 1.4 sounds about right for a swanno

And then you have boats like the S&S34 which goes faster when at speed and/or heeled.

Upright the waterline length is approx 25 ft. This gives a theoretical max speed of 6.5kts.

However, when sailing at speed the stern digs in increasing the water line length to nearer 29ft and speed to 7.2kts.

When heeled the tumblehome increase water line length as well giving a bit more. I think about 7.5kts is the maximum without surfing.

With a decent wind and a good swell/sea behind me I've seen nearly 9 kts on MB. Azzurro has recorded 17 or so kts.

Some good simple info in this link.

www.ss34.org/index.php/the-ss34/technical/#speed

Also, to add the bull in the china shop, water line length hull speed is not a physical constant like the speed of light, its the point where the force required to move the boat faster has become exponentially more difficult and is a defined point of that. I could imagine beefing up sail size, and running downwind, could edge a boat a bit faster by brute force. But I'd love to hear from a naval architect about that. My Spacesailor 24 did a good 10+ knots towed behind a mates V8 ski boat years ago when we were in a hurry. Way past its hull speed

Found this: dmsonline.us/the-truth-of-hull-speed-how-to-break-the-sailing-speed-limit/

MorningBird said..
And then you have boats like the S&S34 which goes faster when at speed and/or heeled.

Upright the waterline length is approx 25 ft. This gives a theoretical max speed of 6.5kts.

However, when sailing at speed the stern digs in increasing the water line length to nearer 29ft and speed to 7.2kts.

When heeled the tumblehome increase water line length as well giving a bit more. I think about 7.5kts is the maximum without surfing.

With a decent wind and a good swell/sea behind me I've seen nearly 9 kts on MB. Azzurro has recorded 17 or so kts.

Some good simple info in this link.

www.ss34.org/index.php/the-ss34/technical/#speed

How can tumblehome increase waterline length? It's not measured along the edge of the immersed area, but from the fore-and-aft length along the water.

I will keep away from water line length and have a go at your question about mast and sails.
Swanson 30 Cutter Rig recently for sale, that the owner replaced the rig with a Swanson 32 rig.

A taller rig means more sail area (than was originally specified for the boat).
This will mean in light conditions you can hoist more and go faster.
As the wind picks up you will need to reduce sail and probably bring the boat back to speed you would get out of the original rig.

The cutter rig could be a large genoa forward and a normal size inner foresail.
This would give you the combinations.
1. just full genoa.
2 just inner sail
but usually not both set at the same time.

If the foreward sail is a jib you will have a combination of;
1. just foreward sail.
2. just innersail
3 both sails.

If they are a genoa forward and an inner jib on roller furling , you then have those combinations.

In general a cutter will not give you extra speed, but a wider variety of foresail combinations.
I think the cutter rig was fitted for ease of handling more than a quest for speed.

My guess is he improved his acceleration to his maximum speed on all points of sail, and it achieved a faster speed in light winds than could have been achieved with the original rig and sails.

The question of acceleration is really tricky.
I think that really depends on sea conditions.
If you tack into steep chop with almost any rig and you will slow down before you take off.
Calmer conditions will allow the boat to pull away better.

gary

Cutters are rarely faster all-round. The best indication is that in most rating rules, the cutter's staysail is unrated and is therefore free area. There is nothing stopping anyone from rigging their TP52 or Farr 40 as a cutter - but they don't because they are not faster all-round. Cutters can be faster on reaches, but they require delicate trimming because the sails interact so much and it's easy for one sail to stuff up the others.
There were many cutter rigs in the early days of sailing and in almost all such classes there was a move to single headsails, which are generally faster.

That's not to say they are not a good cruising rig; the one I've sailed most works very well. But all-round they are not faster.

Jolene said..

MorningBird said..

Chris249 said..

MorningBird said..
And then you have boats like the S&S34 which goes faster when at speed and/or heeled.

Upright the waterline length is approx 25 ft. This gives a theoretical max speed of 6.5kts.

However, when sailing at speed the stern digs in increasing the water line length to nearer 29ft and speed to 7.2kts.

When heeled the tumblehome increase water line length as well giving a bit more. I think about 7.5kts is the maximum without surfing.

With a decent wind and a good swell/sea behind me I've seen nearly 9 kts on MB. Azzurro has recorded 17 or so kts.

Some good simple info in this link.

www.ss34.org/index.php/the-ss34/technical/#speed

How can tumblehome increase waterline length? It's not measured along the edge of the immersed area, but from the fore-and-aft length along the water.

I'm not sure how it works to be honest. As the boat heels the length for and aft increases due to the way the boat sits in the water. It may be that it sits deeper due to the hull shape.
Maybe we have a naval architect who can explain.

I thought it was the stern overhang that lengthens the waterline with heal (lay the boat over and there is less hull overhang ,,, more in the water)

They have a lot of overhang at each end. My recollection was that the hull shape when heeled put more of the overhang in the water. How that is achieved I may have known once, but not anymore.

I haven't looked it up for many years but I believe 25 to 30 deg heel is the optimum. I can tell you it does more than 6.5 kts on the wind inside Pittwater with a fresh noreaster.

Cutter rig on a Swanson 28 will definately slow it down. Cutter rig on large yachts will give some gains on some points of sail. On a Swanson 28 the extra drag will kill the speed.

The 28s haven't raced much but the one we raced when I was a kid was pretty slow. The 42s that have raced were not fast. For example, many years ago when they were new, two 42s raced in the windy 1976 Sydney to Hobart. They were over 25% slower than the first boat of their length, a day slower than the top Cole 43s which are older boats, and 16 hours behind the shorter, older, long-keeled Mercedes III. They were five hours behind an East Coast 31, two to three hours behind a Nicholson 36 (a 1960 design long keel cruiser/racer), half a day behind the first S&S 34, and hours behind several other cruising boats of similar length. A ferro high-freeboard long-keel Endurance 35 was only 2-3 hours behind. Their other races were similar, apart from one good performance when Mick Morris and a top crew of veterans pushed Sunbird home in a windy Mooloolaba race; the 42s typically finished hours behind boats like Currawong 30s, S&S 34s, Swanson 36s, etc; I did a long race on on once, and while "slow" is relative it's true to say they were much slower than the typical displacement cruiser/racer of their day, and of earlier years.

A good buy I reckon. Well done.

To your original question BB.


Can increased rig size and sail plan increase boat speed on a Swanson 30

Did you ask the previous owner?
What did he have to say on the matter?

Congratulations on the new boat.

gary

Enjoy her BB and welcome to the Swanson Family ?? She won't win round the cans or sail past cruiser racers .She is a solid and a sea kindly yacht like all Swanson's

Cheers Jb

Good job BB she will be a great solid boat i nearly bought a 38 recently .