Slowing down for sea state

[Flows]

Subjective question of the year maybe...

Are there any rules of thumb with performance cruising cats on when you slow down in wind chop for comfort based on LWL? Assuming things like bow design potential buoyancy well matched to rig harmonics and numbers that allow you to power up in the light, good wing deck clearance etc.

Eg. Established 2 - 3M swell. Slow the bus down for the cook at:
40ft: 20 knots @45 - 70 TWA 25 knots @110 - 140 TWA
50ft: 25 knots @45 - 70 TWA 30 knots @110 - 140 TWA
60ft: 30 knots @45 - 70 TWA 35 knots @110 - 140 TWA

At the heart of the question is an assumption that the majority of our time we cruise offshore in 15 - 25knts and does this mean that you really need a 50fter to keep going into the last third of the typical conditions without spilling the drinks or is that luxury reserved for 60ft +

Understood that you are averaging faster as you get bigger for the same spot in the performance envelope so slowing down becomes relative. Lets consider Crowther Catanas - Outremer 55Ls - Chris White Atlantics to mark out the sweet spot.

We could also add in a real world 1st standard deviation messy sea state fudge factor.

Ok I have made that complicated enough.

Essentially, how big do I need to not fuss about wind chop in 30knts forward of the beam? What about 25knts? Aft of the beam?

[Chablis 1]

Slowing down too much could also be uncomfortable. The sails needs to be under pressure or they will start to flog and the boat jerk or roll. I feel very comfortable sailing 8kn in almost any conditions, except close hauled, and even faster with the wind aft of the beam. At night, speed below 8kn add more comfort, increased margine of safety and better sleep. Catana 47, Christophe Barreau design.

[Tin Tin]

There is no rule of thumb as the conditions of the sea, the current, the fetch, the depth the wind against swell angle, the wind against current angle, the swell against current angle, the period between waves and so on. Firstly follow the reefing guidelines for your boat then the most important rule, if your wine glass falls over you are going too fast.

[Flows]

All understood there folks, we'll leave current out of it for now, as important as that very much is.

Anyone with blue water experience with 40, 50 and 60 ft performance cruisers want to tweak my initial wind chop, LWL, wine glass vertical hunchimation.

Established 2 - 3M swell. Need to slow the bus down for the cook at:
40ft: 20 knots @45 - 70 TWA 25 knots @110 - 140 TWA
50ft: 25 knots @45 - 70 TWA 30 knots @110 - 140 TWA
60ft: 30 knots @45 - 70 TWA 35 knots @110 - 140 TWA

Or just have a stab at:
how big do I need to not fuss about wind chop in 30knts forward of the beam? What about for 25knts? Aft of the beam?

[BigBeakie]

Are you talking about those windspeeds in a passing weather front situation for an hour or so, or passage making under sustained wind system with associated sea state? Thirty kts of wind, upwind, is alot, and you'll have more than "wind chop" to deal with.

IMO hull design, fore/aft weight balance & keeping weight centrally located, and good sail balance for the conditions are possibly as important as LWL. All things being equal, like anchors, bigger is better.

[Simi 60]

Speaking from experience if you stuff the bows in and get a wall of green over the top I reckon that's a clear sign to put the brakes on for seastate.

If your eyes have been like dinner plates or your buttocks have puckered at any time that is also a clear sign.

Probably should be putting the brakes on before then but fast miles are fun......until they're not.

[chris mac]

I'm on a 42 foot cat. Not a performance model, but fast enough. (42 tpi)
I can't really give you numbers like the question is asking, but for following seas we try to match the wave speed. Get in a trough between and it smooths out the boat. With beam or quarter, it's tough to really say. Wave period makes a big difference. If we need a half hour to cook I would turn and run to calm things down.

[fxykty]

Waterline length trumps pretty much any other factor - a gale for a smaller boat is a fine sailing breeze for a larger boat.

Swell is not a problem until it starts to have breaking tops or the period is too short such that at some speed the boat launches off one and into the next (or buries bows going the other way). 2-3m swell is nothing. 5-7m swell is nothing. 3m swell with breaking faces and vertical backs is awful.

Wind waves are generally another matter. 30 knots TWS can develop 2m chop with enough fetch that either easily handled or with some adverse current and steepening can be horrific.

Also, is there a cross-swell and/or cross-wind waves? Those make pretty much any speed upwind not comfortable. Downwind not so much problem.

Our boat (2003 Outremer 55L) when powered up is happy upwind at 9-11 knots. Slowing down to 7 knots makes a huge difference in comfort, but we actually seldom feel the need to slow down deliberately when sailing upwind. If not powered up then even relatively small waves can be less comfortable, despite the slower speed.

Reaching or running is generally comfortable until the surfing doubles the average speed (say 9-11 knots average and surfing into the high teens and low twenties). Putting additional one or two reefs reduces the average to 8.5-10 knots and limits the surfs to mid-teens - way more comfortable. As opposed to upwind, if not fully powered up does not affect comfort too much, especially if you can control the sails so they don’t slop and slam from side to side.

[dougweibel]

We are not on a performance cat but do sail offshore. Our experience is that we are often more comfortable going faster. 9 kts often feels better than 7 as a powered up rig stabilizes the boat. Friends with performance cats have told us they have slowed down for comfort, but it seems like that meant slowing from the high teens to the low teens so really only an issue for fast sailors on quite fast boats

[Tupaia]

Power to weight ratio, balance, windage, keels and beam. All these factors have an effect on how a boat handles various conditions, far more so that just WLL.


A light powerful boat can be reefed down and still maintain high averages whereas a heavy boat despite its longer WL will always be under pressure.


Similar with windage a boat with a long WL with high freeboard that resembles a shed will be much more uncomfortable, especially going to windward than a low profile boat that is much shorter.



By far the biggest comfort factor IMO is keels or boards. A keeled cat will not be able to go as close to the wind as a cat with boards so will be subject to oncoming waves at a greater angle and have to sustain it for longer.



For downwind a cat, with boards, up, will be able to attain much higher speeds, be much more controllable and more comfortable not just because of less drag but because the CR is very far aft resulting in hardly any need for course correction. A keeled cat on the other hand with small rudders under the same conditions, would need to slowed to prevent the rudders cavitating and the CR from rapidly moving forward making steering unstable and can in worse case result in a 180 (broach).

[catsketcher]

When I taught sailing I was a big fan of listening to the boat. The boat will tell you what to do by how she behaves. The Physics of it is pretty easy - when the accelerations become too great then the crew get grumpy.

I once was asked by a guy who sailed halfway around the world to go out on his cat and look at why the boat could sail well on one tack and not the other. She was a great boat and I could not see any reason for the problem at anchor. When we went out sailing he used the instruments to steer the boat. Telltales stalling, genoa luffing on one tack and full and by on the other. Somehow the electronic wind indicator had shifted 10 degrees one way, I couldn't get why he used instruments in good daylight when the boat was screaming at him to sail properly. Listen to the boat and don't let instruments do anything but be a very rough guide.

The variables of when to slow down are so varied - tide, sea state, angle, time of exposure, day or night, just use your noggin to work it out.

The best accelerometer is your, or your partner's body. It will tell you when to slow down. When we sailed as a family I knew to slow down when the crew complained.

[Montanan]

GEEZ, keep it simple. Just do as the cook or the crew tells you to navigate so as to ride comfortably under various conditions.

[Flows]

All good stuff.

This:

Originally Posted by fxykty

Waterline length trumps pretty much any other factor - a gale for a smaller boat is a fine sailing breeze for a larger boat.

vs this:

Originally Posted by Tupaia

Power to weight ratio, balance, windage, keels and beam. All these factors have an effect on how a boat handles various conditions, far more so that just WLL.

Is the heart of the question. Remember we are eliminating current and just talking wind waves.

We have also removed non performance cruisers and race boats from the list of confounding factors and keeping the how much does LWL impact on comfort at speed limited to boats that can go too fast for comfort while within remaining within their load limits. So boats with boards and BNs in the 1.14-1.18 when typically loaded range.

Again the purpose of the question is to inform on LWL impact on comfort in that 25-35 knot range on a boat that will go fast if you let it.

So for boats with a cruising weight BN of 1.16 ish how much does LWL matter and how much wider is the "don't need to slow down" wind range for a 40 vs 50 vs 60.

We don't need precise calcs just good enough for government work hunches from folks that have been at sea on 40 though 60ft performance cruisers.

[fxykty]

We have a 54 footer with relatively fine ends, especially the sterns, which are much narrower than current designs. We wouldn’t be any shorter ever, and possibly longer at certain times (not when berthing!).

We don’t have experience on other, shorter, performance cats (I won’t count offshore racing an open bridgedeck 40 footer, as that was uncomfortable due to speed in almost every sea state), so can’t compare. But I can say that we have never slowed down for comfort, cooking or sleep when sailing upwind (that must be a monohull thing). We have deliberately slowed down for comfort by deep reefing in moderate conditions when broad reaching and downwind to prevent the micro movements associated with excess high speed surfs. It also provides more gust resilience, which is comforting.

Sea states confound a single wind speed metric, so your question cannot be answered except as ‘it depends’.

[Tupaia]

Originally Posted by fxykty

Sea states confound a single wind speed metric, so your question cannot be answered except as ‘it depends’.

Couldn't agree more.


It also depends on how you judge comfort. If there are no monitory restraints then the ideal size for someone will be determined by location, experience and circumstances.


So not quite sure what you are trying to accomplish by such a question in isolation.


Are you looking to own a cat?