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Old 25-01-2008, 01:07   #301
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Your in the Engineering phase again which I do have some experience of.
First I would say keep a note book on engine runs and note boat speed, engine revs, wind speed and direction.
Your (nautical)miles per gallon is speed divided by gallons per hour.
Shouldn't take long to work out your economical speed and your hurry along costs per mile. That will give you a good ides of how far your boat will could go on the fuel on board and whether it will go futher if you slow down a bit.
I suspect, not tested, that most economical speed is between two thirds and three quarters of the top speed. DATA PLEASE.
Oh the wind. Obviously it makes a difference, by making a note you'll have some idea of how much difference it makes. If the difference is big your prop may not be right.
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Old 06-02-2008, 14:28   #302
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News from Willmar USA

Mahe 47 "OPTIONS" with owner Mark on board made it to Antigua last monday after a fast crossing from the Canary Islands .They stopped in Cap Verde and ,I think,had the time of their life .
I spoke with Mark after they arrived and he had only good things to say ( few warranty items )
So he is happy and the WIllmar team is happy.Only wish that we could spend as much time on the water as some of our owners

On the other hand Irie Cat was supposed to be our show boat in Miami.At the last minute we learned that it will not happen as they had other commitments .....surprise surprise.
So we had to fall back on our option B .Luis 's boat " COOL CAT" will be in
It is a 2007 model without the new portholes ...
Anyway we will welcome you all in Miami .February 14 to 18 at Bayside Marina dock C22
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Old 06-02-2008, 14:53   #303
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Quote:
Originally Posted by Therapy View Post
I keep seeing this kind of evaluations for marine stuff and still do not get it.
I know currents etc make a difference in SOG but mpg is a more real figure to me.

If one burns a little more fuel but goes faster then the total time the engine is run and the amount of fuel burned could be the same.............in many instances.........what am I missing...........???
Besides the fact that for each setup there is an optimum that takes a long time to find.
Therapy; there are a couple of basics regarding fuel consumption and boat speed for boats in displacement mode, i.e. NOT planing, and Catamarans NEVER plane!

First there is hull speed, which can roughly be calculated as:

1.34 x SQRT Lwl. So for a 36 ft boat, the hullspeed will be around 1.34 x SQRT36 = 1.34 x 6 = 8 knots. This is the point where there will be a resistance "hump" that is very inefficient to go beyond when motoring.

The next "fact" is that fuel consumption for a motor/propeller on a boat in displacement mode can roughly be calculated, using: Consumption = Constant x n e3. ( n is rpm) So if you know your consumption at one speed, you can roughly calculate what it will be at another.
Basically this means that to double the revs your consumption will be 8 times higher. This is not entirely true, as alternator loads, fricton losses etc. are relatively higher at lower speeds. Also windage, waves, wind speed and wind direction play a role, and are part of the Constant for a set of defined conditions.

I hope this clears things up a bit.

Regards

Alan
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Old 06-02-2008, 16:34   #304
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I think Therapy's point was simply that while gph implies some sort of reasonable progress under some defined set of circumstances, it doesn't by itself tell you anything about how far or fast you can go. It simply tells you how long you can run the engine for a given supply of fuel under those conditions. Mpg doesn't tell you anything about speed either, but it tells you exactly how far you can go for a given supply of fuel. I think gph was probably popularized in the context of big twin engine cabin cruisers with embarassingly low mpg - even then it was generally and helpfully expressed as gph @ x knots. It is certainly true that the variables of wind, current, tide, seas, etc. make an EPA style mpg rating for boats kind of silly. That doesn't mean that it's not a uselful number for a given boat on a given trip under given conditions.
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Old 06-02-2008, 18:05   #305
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I think Therapy's point was simply that while gph implies some sort of reasonable progress under some defined set of circumstances, it doesn't by itself tell you anything about how far or fast you can go. It simply tells you how long you can run the engine for a given supply of fuel under those conditions. Mpg doesn't tell you anything about speed either, but it tells you exactly how far you can go for a given supply of fuel. I think gph was probably popularized in the context of big twin engine cabin cruisers with embarassingly low mpg - even then it was generally and helpfully expressed as gph @ x knots. It is certainly true that the variables of wind, current, tide, seas, etc. make an EPA style mpg rating for boats kind of silly. That doesn't mean that it's not a uselful number for a given boat on a given trip under given conditions.
Righto!

A simple number. I know there are more variables on water than on land!

When I (if ever since this week was full of bad news for the future) get a boat, one of the things I will know is how many miles per gallon I will get given a set of parameters, ie light wind, low seas, bla bla, etc.

Thanks.
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Old 13-03-2008, 12:38   #306
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Thumbs down Catamaran MAHE 36

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I just was wondering if they are any menbers on this forum who have ordered the new FP mahe 36'.it would be interesting to exchange thoughts about the boat.
Hello, I'm french and don't speak very well, so Excuse me, I can speak a lotabout the firm Fountaine Pajot, and I am very décue by the building site, we do not have any service after sale. The leaders promised to us to occupy ourselves of our boat which is not finished and since 1 year no result. It'"s a pity....
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Old 13-03-2008, 15:14   #307
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Yr message was not quite clear to me.. You can write in french if you prefer I will translate for those who are interested. Disappointed deçu for what ..

Yeloya
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Old 13-03-2008, 17:14   #308
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Ngorei

Yr message was not quite clear to me.. You can write in french if you prefer I will translate for those who are interested. Disappointed deçu for what ..

Yeloya
I'm a thinkin he/she said the boat was supposed to be in his/her posession a year ago and still is not. leaders (Management) not responsive either. Please translate full story.
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Old 14-03-2008, 07:01   #309
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Ngorei

Yr message was not quite clear to me.. You can write in french if you prefer I will translate for those who are interested. Disappointed deçu for what ..

Yeloya
I think what she is trying to say is that she is diappointed in FP as a company, their after sales service is non-existent, the management don't want to know their problems ie that after a year of complaining and them promising nothing has been done to rectify the faults.
I think they already have the boat because if you go into their profile they show a picture of their boat - maybe I am wrong, but whatever she is saying is that they are not happy with FP.
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Old 14-03-2008, 07:07   #310
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Fountaine Pajot

We are the importer and dealer for the USA of Fountaine Pajot and I must say that the shipyard has been working very closely with us in solving warranty problems.The procedure is to have the repairs details and costs send to your dealer then approved by the yard before starting work.
So far Fountaine Pajot has been standing behind their Mahe and the boats are aging very well with minor problems
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Old 14-03-2008, 08:38   #311
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We are the importer and dealer for the USA of Fountaine Pajot and I must say that the shipyard has been working very closely with us in solving warranty problems.The procedure is to have the repairs details and costs send to your dealer then approved by the yard before starting work.
So far Fountaine Pajot has been standing behind their Mahe and the boats are aging very well with minor problems

Could you enlighten us at to the nature of these minor problems? I felt that the boat was very "squeeky" on a test sail, alot of flexing around the nav table/galley area, as they for some reason have chosen not to join the furniture to the hulls
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Old 14-03-2008, 08:44   #312
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Mahe

we have boats which have crossed the Atlantic on their own bottom.Some required cosmetic repairs on dents or gel coat .
We had a few leaks as well but nothing drastic
Flexing .They do flex .Seems to be the nature of lights and fast cats; and creaking or squeaking seems to be a problems on boats with an overtensionned rig
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Old 14-03-2008, 08:46   #313
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Not joining furniture seems to be a modern PROD'N short cut. Not a problem if it was designed like that rather than a short cut. And don't put the joins in afterwards or you'll create stress points. I think the furniture carcases are installed before the top goes on. Any one seen this at the factory?
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Old 14-03-2008, 08:48   #314
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Indeed .That was part of the design .
Furniture goes in glued then the top goes on
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Old 14-03-2008, 08:57   #315
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See Fastcat for his silent rig approach. He avoids metal/metal contact in rig attachments and claims a quiet boat is much less stressful. He's got a point.
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