Heavy vs Light Displacement

[Joli]

Well. A light boat with a nice SA/D changes dramaticly when carrying cruising gear. As an example, the J 37 SA/D changes from 21 to 17 with 5k cruising payload while the Gozzard 37 SA/D changes from 18 to 16. A heavier boat carries a bigger rig and is less affected by payload. So the reasoning to build a light cruising boat with a small rig doesn't work unless you build a very large boat where payload is a small percentage of overall weight.

Let's throw out a question. The J37 rates 69 in phrf, the Centurion 47 rates 75 in phrf. On the race course, who will finish first most of the time? When cruising and carrying gear who will have the shorter passage time most of the time?

Originally Posted by Paul L

The amount of weight that will cause a boat to drop one inch at the water line has nothing to do with the displacement of the boat. It only has to do with the area of the plane that intersects the water.
Weight for a 1 inch drop:
Hans Christeian 38 1,444
J/37 1,427
Tayana 37 1,274
Alberg 35 829


Paul L

[Cheechako]

I think the only apples to apples comparison is 2 boats with the same hull shape. One built loaded with teak, bronze/stainless winches and portlights, heavy layup and the other built with higher tech resin infused hull, minimal teak, aluminum winches etc. Then how do the numbers come out? Something interesting: when I bought my 42 ft catamaran, I moved off my Passport 47 mono. The boats were at the same dock next to each other. I literally transferred all my stuff from the Passport to the cat right across the finger pier. The Passport came up about 5 inches on the water line. The cat went down about an inch +!
Yea the Tayana 37 is similar to the HC 38, but much less encumbered with the weight I mention in the post above. Also, the biggest sail I used (Lazy) was a 120 high cut. However, I dont think your Tayana will be doing 3 knots in 5 knots in a 3-5ft seaway! We cruised with a T37 "Solitude" :>)

[Paul L]

Originally Posted by Joli

Well. A light boat with a nice SA/D changes dramaticly when carrying cruising gear. As an example, the J 37 SA/D changes from 21 to 17 with 5k cruising payload while the Gozzard 37 SA/D changes from 18 to 16. A heavier boat carries a bigger rig and is less affected by payload. So the reasoning to build a light cruising boat with a small rig doesn't work unless you build a very large boat where payload is a small percentage of overall weight.

Yep, weight does nothing good for sailing. Even with your numbers above, the J will still have more drive from its sails, 17 vs 16. I'd suspect that most anyone who cruises a medium weight boat like the J would be more careful in watching what gets added to the boat than a typical cruiser, i.e keeping the weight added down. I think a lot of cruising boats would sail a whole lot better if the added weight was watched closer. That doesn't mean you don't have good anchoring gear etc, it just means that you understand the trade-offs on what all that weight and junk is doing to your sailing. And what that poor sailing does to the engine hours.

I'm not sure what you mean by small rig. The J/37 has a 54 ft air draft. About the same as a Tayana 37.

Originally Posted by Joli

Let's throw out a question. The J37 rates 69 in phrf, the Centurion 47 rates 75 in phrf. On the race course, who will finish first most of the time? When cruising and carrying gear who will have the shorter passage time most of the time?

I don't really get this comparison. You want to compare a 47 boat to a 37 ft boat? PHRF is not a good comparison if you are looking at something like a tradewind passage.

Just so its clear, I have no problem with heavy cruising boats. You can cruise in just about anything -- and it has been done. Every boat will have a whole list of tradeoffs. The only reason I reply to these types of threads is because I disagree with those who say that you can only safely cruise in a heavy boat.

Paul L

[sneuman]

Originally Posted by Cheechako

I think the only apples to apples comparison is 2 boats with the same hull shape. One built loaded with teak, bronze/stainless winches and portlights, heavy layup and the other built with higher tech resin infused hull, minimal teak, aluminum winches etc. Then how do the numbers come out? Something interesting: when I bought my 42 ft catamaran, I moved off my Passport 47 mono. The boats were at the same dock next to each other. I literally transferred all my stuff from the Passport to the cat right across the finger pier. The Passport came up about 5 inches on the water line. The cat went down about an inch +!
Yea the Tayana 37 is similar to the HC 38, but much less encumbered with the weight I mention in the post above. Also, the biggest sail I used (Lazy) was a 120 high cut. However, I dont think your Tayana will be doing 3 knots in 5 knots in a 3-5ft seaway! We cruised with a T37 "Solitude" :>)

true, but the light displacement boat will probably be a lot less comfortable in those conditions and depending on the point of sail will be just as easily stopped in her tracks by the swell. Luckily, here in the Chesapeake (short fetch) that seastate is typically accompanied by a fair amount of wind.

[barnakiel]

Originally Posted by Bloodhound

To my mind, heavy displacement = comfortable and sea-firiendly, albeit slower than a racer in light air. Light displacement = faster in light air with less sail but very uncomfortable for anything longer than a few hours. In heavy air, equal LWL will have equal speed but heavy = comfortable. I like comfortable.

Well, yes - but heavy disp boats tend to roll like hell downwind and to many cruisers downwind is 90% of their sea time. A beamy light thing sails downwind best.

I have a mid-disp boat but sailed some ultra-lights and downwind they are best. Surprisingly, upwind they beat the heavy clunker too. I did not believe this untill I sailed a Farr 40 @ 7 knots in a chop that would stop my boat dead.

b.

[galleyslave]

Not quite true. I used to sail a Nich32, mostly singlehanded. The problem with light displacement boats is not light conditions but that you have to start reefing so early or they will become unmanageable. I used to pull the next reef in on the Nich when the lee rail started to drag in the water and slow her down, not because she was becoming difficult to manage- just uncomfortable and putting a lot of strain on her gear. Undermanned, light displacement boats usually disappeared astern when the wind piped up forward of the beam.

Obviously, the situation is different when a light displacement boat is kept going by its electronics, not inherent stability but, when the going gets tough, I want a boat that will look after me, not the other way round.

[sneuman]

Originally Posted by barnakiel

Well, yes - but heavy disp boats tend to roll like hell downwind
b.

This is not my experience. It depends on the seastate, but in general, my experience is that lighter = more wallow down wind.

When it comes to reefing and how early one is required to do it, it depends on a lot of other factors, such as hull shape and sail area. My Tayana for example, is a "reef early" boat (15 kts), which surprises most people she's such a heavy gal (22,000 lbs). It's because she carries a lot of sail, yes, but more importantly it's the hull form that is slight on initial stability. It heels a beat on a beam reach or higher, but stabilizes nicely at about 12 degrees. By the way, that "tender" hull shape just happens to be the same hull shape that makes her exceedingly comfortable in a bumpy seaway. Like they say, all boats are compromises.

[Joli]

Why would you head dead down if the sea state makes it uncomfortable? Why not head up a bit and press the boat? Set the assy and pull the apparent or if it's blowing the dogs off the chain do the same with a jib.

Regarding the Farr40, they don't sail downwind. At 6 true they sail 140.5 twa or 78.6 awa. (ie they reach).

Oops, forgot this, see page 7. http://www.farr40.org/pdf/farr40vpp.pdf

Originally Posted by barnakiel

Well, yes - but heavy disp boats tend to roll like hell downwind and to many cruisers downwind is 90% of their sea time. A beamy light thing sails downwind best.

I have a mid-disp boat but sailed some ultra-lights and downwind they are best. Surprisingly, upwind they beat the heavy clunker too. I did not believe this untill I sailed a Farr 40 @ 7 knots in a chop that would stop my boat dead.

b.

[Joli]

The problem with a light boat carrying an appropriate sail plan for the light boat is load carrying capability. The was the question posed by the OP.

The comparison I drew drawn between a faster medium weight boat (J37) and heavier but slower boat (Centurion 47) is to highlight how load affects boat speed. I think you will agree that the J37 in race trim is faster around a W/L course but when loaded with cruising gear the Centurion is going to be faster.

Light fast boats are not fast when loaded up for cruising.

Originally Posted by Paul L

Yep, weight does nothing good for sailing. Even with your numbers above, the J will still have more drive from its sails, 17 vs 16. I'd suspect that most anyone who cruises a medium weight boat like the J would be more careful in watching what gets added to the boat than a typical cruiser, i.e keeping the weight added down. I think a lot of cruising boats would sail a whole lot better if the added weight was watched closer. That doesn't mean you don't have good anchoring gear etc, it just means that you understand the trade-offs on what all that weight and junk is doing to your sailing. And what that poor sailing does to the engine hours.

I'm not sure what you mean by small rig. The J/37 has a 54 ft air draft. About the same as a Tayana 37.

I don't really get this comparison. You want to compare a 47 boat to a 37 ft boat? PHRF is not a good comparison if you are looking at something like a tradewind passage.

Just so its clear, I have no problem with heavy cruising boats. You can cruise in just about anything -- and it has been done. Every boat will have a whole list of tradeoffs. The only reason I reply to these types of threads is because I disagree with those who say that you can only safely cruise in a heavy boat.

Paul L

[sneuman]

I think Joli's point is crucial. Boats are designed to sail on their waterline. I read Bob Perry's book a few months ago and he tells a few stories of the relief he experienced (as any naval archietect apparently does) when hull #1 of a new design is set in the water and floats on the bootstripe. That's because if it doesn't, all the other calculations and expectations are thrown into question.

Most real cruisers are designed to keep the waterline - or something very close to it - when fully loaded. That means 800-1,000 lbs of water, something close to that for fuel, as well as food, clothes, tools and 2-4 adults.

[Cheechako]

Yea, I learned a lesson motorsailing down the Chesapeake one time. I was headed for Norfolk against a nasty 3-5 ft chop in my Passport 47. The P47 has a nice long water line but is really heavy... much heavier than the design specs showed. (which isnt untypical by-the-way) I was trying to pound through it and I see a white spot appear behind me. It wasnt very long before a Hunter (?) 40 (argghh!) caught up and went motoring past me at about 7 knots. The difference? Being a lightweight, he was riding mostly on top of the chop, I was was plowing through the chop..... each wave slowing my progress....

[sneuman]

Originally Posted by Cheechako

Yea, I learned a lesson motorsailing down the Chesapeake one time. I was headed for Norfolk against a nasty 3-5 ft chop in my Passport 47. The P47 has a nice long water line but is really heavy... much heavier than the design specs showed. (which isnt untypical by-the-way) I was trying to pound through it and I see a white spot appear behind me. It wasnt very long before a Hunter (?) 40 (argghh!) caught up and went motoring past me at about 7 knots. The difference? Being a lightweight, he was riding mostly on top of the chop, I was was plowing through the chop..... each wave slowing my progress....

Interesting. One mitigating point (although you did say you were motorsailing) might be that the Hunter's SA/D borders on the racer, while your Passport falls decidedly on the "cruiser" side. You could have put 20% more weight inside before moving the waterline too.

On the other hand, at roughly twice the displacement (the Passport) only gets you 20% more load-carrying capacity. It's all a tradeoff.

Fortunately, once you're offshore you will rarely if ever find the short, speed-sapping chop you get on the Chessie -- the wave period is much greater.

[S&S]

Cheechako:
It may be more of a hull shape thing: I was on a Morgan Giles 42 (RN sail trainer) in the Channel with about a 10' chop. we went to windward great with her slicing through the waves. She was typically narrow (10'6" beam) for British boats of her vintage

[Cheechako]

The P47 was generally a pretty good offshore boat. But it was an eye opener in those particular conditions. The Hans Christian 38 would have been wallowing terribly.... Bow I spent a very frustrating time one day trying to get from Grenada to the grenedines in that boat. 3-5 foot waves left over from a blow the night before, minimal wind, boat just wouldnt move sailing or motoring!

[sneuman]

Originally Posted by Cheechako

The P47 was generally a pretty good offshore boat. But it was an eye opener in those particular conditions. The Hans Christian 38 would have been wallowing terribly.... Bow I spent a very frustrating time one day trying to get from Grenada to the grenedines in that boat. 3-5 foot waves left over from a blow the night before, minimal wind, boat just wouldnt move sailing or motoring!

Were you in a position to either tack or jibe parallel to the wave train?