optimum speed for fuel economy m26

[BOAT]

It's true, I don't know about boat design, but I saw the pictures of the fast boats and like you said they had those little tabs on the keel and stuff. I just thought it was neat. As for the racing part - I was in lots of regattas when I was a kid and never let the fact that I sailed a fat pig stop me from racing. I even got a few trophies. I did not know I was supposed to be slow, so since no one told me I was not slow.

What happens to a MAC when you trim the DB? (Beats me) Mastreb is way smarter than me so I pose the thought - he knows what will happen. There is other stiff I was thinking about too - so I want to know what will happen.

I guess the shoes don't make the cow any faster.

How about a dagger board with a bunch of lead in the end of it? Would that be helpful?

(Fold out wings on the dagger board that you can pop out by pulling a rope??) just sayin' you guys know us California people are out there - I'm just being myself.

[K9Kampers]

How about a dagger board with a bunch of lead in the end of it? Would that be helpful?

Another archived conversation, and I think the infamous black Mac 26M has a lead-bulb DB.

As for racing, who (boat) is the intended competition?

I belong to a trailer sailing group of mostly Macs. On a cruise along the coast of Maine, we were in a slow, light wind convoy enroute toward an anchorage several hours away. I was toward the rear of the line when I noticed I was gaining on, then passing the boat ahead of me. Then the next and the next,... The wind started picking up and I eventually became the lead boat, accelerating away from the pack! All under sail, motor up, k-y-n! I was about 45 minutes ahead when the next of the group reached a certain waypoint. I was zigging a multi-tack course while they zagged straight by dropping sail & motoring the rest of the way. Needless to say, I was last to reach the anchorage, but for a while, I was the fastest under sail. What was I doing different from the others? I call it The Sudoko Manuever. When the breeze was just so light, I had my foot on the wheel while doing Sudoko puzzles when I started accelerating. Best guess is my boat was the lightest, modding & equipped & singlehanding.

The common theory on hull speed is a formula based on waterline length, tho there are designs that aren't limited by that theory. Hull shape and light weight are other factors that can affect speed.

[seahouse]

the most efficient operating speed for a boat at low speed, and that speed is about 4 knots on my boat, as determined by my chart-plotter's maximum range calculation from my engine cable's consumption data.

This is not what I would expect to see (I would expect lower), especially with an E-tec, which has ECM-optimised engine management at low rpm; and it doesn't coincide with kurz's observations. Could it be due to a possible error in the readings because of the very low fuel flow involved? Or other external factors coming into play, such as current as mentioned earlier? Or any other possible sources of error to suggest (in either sets of data)?

[Tomfoolery]

Make sense?

Completely. You've put into words what my gut tells me, but never thought through. Thanks.

[drams_1999]

I agree with tkanzler......thanks Mastreb!

[mastreb]

the most efficient operating speed for a boat at low speed, and that speed is about 4 knots on my boat, as determined by my chart-plotter's maximum range calculation from my engine cable's consumption data.

This is not what I would expect to see (I would expect lower), especially with an E-tec, which has ECM-optimised engine management at low rpm; and it doesn't coincide with kurz's observations. Could it be due to a possible error in the readings because of the very low fuel flow involved? Or other external factors coming into play, such as current as mentioned earlier? Or any other possible sources of error to suggest (in either sets of data)?

Hi Brian: It's quite possible, since I don't have an instrument to mesure current, and I only took this reading once. San Diego bay has a relatively large tidal change every day and currents come into play routinely. It would also be affected by windage as well.

The absolutely correct way to determine it would be to run a triducer, anemometer, and EMM engine cable all to a data loger and track at least one large loop at 2 knots and 5 knots, then you could interpolate the absolute correct number.

[niel passet]

check Flow Network K F R acrylic rotameter flowmeter taper bore with float from ackwourth GA for measuring relative fuel flow without instrumentation Niel Passet Mahe Seychelles

[niel passet]

try flow network KFR acrylic rotameter taper bore flowmeter with float at Ackwourth GA niel passet mahe seychelles

[Boblee]

Crikey five pages on a subject that could be likened to argument of the length of a piece of string, I think I commented somewhere way back and can't be bothered reading all the technical methods of working out optimum fuel economy but there are too many variables to even think about it.
If you want the most economic revs for your boat do it by simply running your boat at X revs for Y time at as close to similar conditions as you can get and then change the revs for the same time until you find the optimum economy for your choice of revs, this will not tell you the economy with a 20knot gale blowing and a 6m tide running the same direction but it will give you a reasonable idea of what it will do if you use the most efficient rev range for a new time under those conditions actually nearly the same formula you would use to find out the length a piece of string needs to be.
Reminds me of a local maths teacher who asked students to calculate how big a hole he needed to dig to bury an underground fuel tank for a certain amount of fuel , unfortunately for him he was in a rural area and when he was told you would buy a tank to hold that amount and then dig a hole 6-12" bigger all round to infill and allow for cover the teacher called the kid a smartarse but obviously smarter than the teacher.
Sometimes a practical approach is better.

[DaveB]

I agree and original poster ansered his own question 5 pages after he posted and most of us gave fuel consumptions at variable speed and wind.wave conditions.
Fuel flow meters are for the hungry Weekend warriors fast Cats .
Fuel spent for me in one year dosn't come close to insurance for my boat.
And I have year round Cruiseing in SW Florida.
What I need is a beer flow scan in my system so it doesn't cost more than the fuel bill, fuel has to go down to $1 a gal me thinks.
Dave

Crikey five pages on a subject that could be likened to argument of the length of a piece of string, I think I commented somewhere way back and can't be bothered reading all the technical methods of working out optimum fuel economy but there are too many variables to even think about it.
If you want the most economic revs for your boat do it by simply running your boat at X revs for Y time at as close to similar conditions as you can get and then change the revs for the same time until you find the optimum economy for your choice of revs, this will not tell you the economy with a 20knot gale blowing and a 6m tide running the same direction but it will give you a reasonable idea of what it will do if you use the most efficient rev range for a new time under those conditions actually nearly the same formula you would use to find out the length a piece of string needs to be.
Reminds me of a local maths teacher who asked students to calculate how big a hole he needed to dig to bury an underground fuel tank for a certain amount of fuel , unfortunately for him he was in a rural area and when he was told you would buy a tank to hold that amount and then dig a hole 6-12" bigger all round to infill and allow for cover the teacher called the kid a smartarse but obviously smarter than the teacher.
Sometimes a practical approach is better.

[K9Kampers]

[yukonbob]

I think the more important thing here is no matter what we get for fuel economy, its a hull of a lot less than most other boat our size.
And Dave, if you find one of those beer flow systems let us know. I'm sure a bunch of us could use one

[Boblee]

yukonbob
[quoteits a hull of a lot less than most other boat our size.][/quote]
Actually it depends if kept at hull speed our boats are far more economical than similar sized powerboats and probably more so to other sailing boats at higher speeds but whether you are happy to idle along at hull speed or get up on plane or even stay somewhere in between will depend on how much fuel you want to use or in some cases (wind/tide etc) if you want to make any forward progress at all or just anchor and read a book while waiting.