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Old 31-01-2016, 10:42   #16
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Re: How much does crew weight affect cruising speed.

Never tried to put my Saint Bernard on the rail, although I do try to keep him on the windward side.
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Old 31-01-2016, 10:44   #17
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Re: How much does crew weight affect cruising speed.

Quote:
Originally Posted by OldFrog75 View Post
Given there are so many smart people here, and I'm too lazy to read a physics book or search for horsepower ratings (for a given LWL, Ballast, Displacement and Sail area), how much does the weight of additional crew affect the boat speed of a "typical" cruising boat?

My intuition tells me, not much.

We not typical. We are 36 tons, 58 feet, 15'-7" beam. It doesn't even matter when we add 380 gallons of diesel and 280 of water. The boat doesn't budge when we step aboard.

This will vary a lot by the boat type.

When I raced a 37' Heritage One-ton many years ago crew weight & distribution was critical. Crew on the bow was a definite speed penalty. We removed the heavy sails on light air days. Heavy crew had to line up aft.

On my Tornado Cat, weight must be well aft in power. In light air, weight goes forward to left the flat transoms out and increase the water line.
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Old 31-01-2016, 11:03   #18
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Re: How much does crew weight affect cruising speed.

If you have adequate HP, it does not effect speed. That is only governed by your waterline length. Weight could effect your time to get to hull speed though.
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Old 31-01-2016, 11:28   #19
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Re: How much does crew weight affect cruising speed.

Well the real answer is none! You said cruising speed not max speed so any boat will maintain cruising speed with a reasonable wind unless grossly overloaded. All that happens is you set a few extra feet of sail area. Also given that cruisers generally carry 1-2tons of stores and provisions unless you take the entire line back team crew weight is insignificant.
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Old 31-01-2016, 11:49   #20
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Re: How much does crew weight affect cruising speed.

As my sailing freinds & I call it "movable ballast", and it works like this:
On those 'windy days, the moveable ballast is up on the windward rail. Get the boat to stand up.

Light air days, down to the leeward rail, get the boat to heel and get some shape in the sails.

And lastly, extra weight lowers the boat's waterline, therefore a longer waterline (we are talking traditional hulls with overhangs) and as we know longer waterline more boat speed.

The best part is, drink more beer.
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Old 31-01-2016, 11:52   #21
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Re: How much does crew weight affect cruising speed.

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Originally Posted by OldFrog75 View Post
Given there are so many smart people here, and I'm too lazy to read a physics book or search for horsepower ratings (for a given LWL, Ballast, Displacement and Sail area), how much does the weight of additional crew affect the boat speed of a "typical" cruising boat?
===

Of course it depends on the boat, the weight of the crew, where the crew sits and strength of the wind. The PHRF committee of Western Long Island Sound used to figure that an extra 350 pounds on the weather rail would increase boat speed by 3 to 6 seconds a mile in moderate winds of 8 to 10 knots. That's an approximation of course. How fast is 6 seconds a mile? At 5 knots average speed, the difference is about .05 kts. That's a big difference to a racing boat but not much for cruising.
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Old 31-01-2016, 12:04   #22
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Re: How much does crew weight affect cruising speed.

Depends a lot on whether the extra crew is beating the drum, or thrashing the bullwhip, doesn't it?
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Old 31-01-2016, 12:04   #23
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Re: How much does crew weight affect cruising speed.

Hope the weather improves...though it is not cold.
Showers 'till Thursday!
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Old 31-01-2016, 12:19   #24
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Re: How much does crew weight affect cruising speed.

by the math, it matters. in practice, it makes no real difference. in racing on ultralight, high performance boats an extra body or 2 really can affect things. not really the case with cruisers.
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Old 31-01-2016, 12:29   #25
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Re: How much does crew weight affect cruising speed.

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I can feel the difference of an extra crewman on my 2800 pound 8.5 meter cat.

It is worse with 6 more and a cooler full of beer!
And on my 1250 pound 9 meter cat you could tell if they leaned forward!

My current cat is slower (8500 pounds, 34 feet), but I still mentally attach $ value to added weight (how much more would I have paid for a lighter boat with the same strength?).

The difference between just me and 4 with cruising stores is perhaps 0.1-0.5 knots, depending on speed (practically nothing below hull speed, more as we get into double digits. It also matters where the weight is (not just windward/leeward, but fore/aft--dragging transoms are slow).
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Old 31-01-2016, 14:34   #26
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Re: How much does crew weight affect cruising speed.

Quote:
Originally Posted by OldFrog75 View Post
Given there are so many smart people here, and I'm too lazy to read a physics book or search for horsepower ratings (for a given LWL, Ballast, Displacement and Sail area), how much does the weight of additional crew affect the boat speed of a "typical" cruising boat?

My intuition tells me, not much.

Ok, let me give you a quite specific answer

Let's pick an X37 as your 'typical cruising boat'. A VPP I have says it will do 7.5kts in 10 kts of breeze at 90 degrees. If you add 500lbs of displacement. The VPP estimates it will be slowed down by .1 kt (to 7.4kts).

Now that assumes the extra 'weight' does not hike and just sits in the same place on the boat. If the weight hikes, then extra weight can even speed up the boat when the breeze is stronger.
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Old 31-01-2016, 14:52   #27
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Re: How much does crew weight affect cruising speed.

It is in my unfortunate experience that it is the quality of crew not the quantity that has a greater affect on my yacht
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Old 31-01-2016, 17:47   #28
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Re: How much does crew weight affect cruising speed.

Very much-- known for a long time--
when the Wikings cruised the world
they throw useless guys overboard
if they where in a pinch
try it
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Old 31-01-2016, 17:58   #29
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Re: How much does crew weight affect cruising speed.

On our 19ft ODay 20, the weight of five adults was rather significant as an effect on performance. On our Oyster 53, five adults isn't even noticed.
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Old 31-01-2016, 20:20   #30
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Re: How much does crew weight affect cruising speed.

Quote:
Originally Posted by OldFrog75 View Post
Given there are so many smart people here, and I'm too lazy to read a physics book or search for horsepower ratings (for a given LWL, Ballast, Displacement and Sail area), how much does the weight of additional crew affect the boat speed of a "typical" cruising boat?

My intuition tells me, not much.

ANY weight does make a difference on any boat. But wiuth what many people call a cruising boat, and others call "crab crushers" - a full keel heavy boat, like a Hans Christian 38, an extra person or three isn't going to make any significant difference. But with my Cal 39 in an 18 knot breeze I'd want 3 or 4 on the rail on the upwind legs - and I'd like to jettison them (except the rules don't allow that in a race) on the downwind legs.

Weight increases the wetted surface thus increasing the resistance ad slowing the boat, On the other hand, additional crew on the upwind legs can provide necessary movable ballast to keep the boat "more level" and thus usually faster. Also more crew can provide additional hands to get things done faster. Many things are very slow to accomplish when singlehanding.

An interesting story, I don't know if it's true, is that in preparation for a circumnavigation race Paul Cayard, in an effort to make the crew understand that weight is critical, required them to shorten the handles on their toothbrushes. And Paul won that race.
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