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Old 09-06-2010, 00:25   #1
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Question Performance Question

Hello evey one
I have a 36 ft Roberts and am updating to the dark side a Catamaran, I'm looking at a 35 or 38 ft Factory built boat Fountaine Pajot or Maxim or Nauticat still looking.
My question is are cats like momo's ie; longer waterline more speed ? in otherwords is a 38ft cat faster than a 35ft cat weight and sails being equal.
Any body out there have one of these boats and can you give me an idea of what sort of performance to expect. I'm going over to Caribean or FT Lauderdale and sailing one back so I'm interested in planning my voyage legs and distance traveled is critical.
ps; Love to talk with an owner of a Fountaine Pajot about what is the boat realy like and are 20hp to small I'd prefer 27-30hp am I correct in thinking that 18-20 to small?

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Old 09-06-2010, 01:46   #2
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Hi Laurie,
I do not own a cat but know a few who do - and others who've built them.
From all I've heard weight is a more important factor in the speed of any cat which is possibly what the carbon Gun Boats seem to fly faster than a longer but heavier mono maxi.
I am pretty sure you'll find someone who has experiecne of both styles of boat and can give you more precise rationale - and good luck with the voyage.

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Old 09-06-2010, 02:46   #3
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Hi Laurie,

Just a few comments on the FP 38'.
The Darkside is traditional/emotional. The upside is real. I just got back from the Bahamas on my FP 38' sailing and anchoring where monos fear to tread. Longer waterlines usually mean more speed and as Swagman states weight is an issue with some speed loss on a Cat. I find the loss very minimal and not noticeable enough to outweigh the benefits of space, comfort, and stability. I was sailing 7.5-10 knts with 200gal. water, 300' of chain, 65 gal. of fuel, carrying on the davits a 11.5' RIB with an 18hp outboard etc. in 18-20 knts of wind. I don't carry light wind sails so it takes about 7-8 knts of wind for me to see substantial movement.
I have the two 18hp Yanmars. I can make a comfortable 7-8 knts with both engines running at 2600rpms. 6-7 knts with one engine at 2900-3200rpms. It will do 9.5 knots with both engines, but the stern starts to bury after 8 knts and the boat begins plowing through the water reducing fuel economy for little gain. Larger engines on this boat would in my opinion be over kill and a waste. Moving up to a 40 foot plus Cat would be a different story and the next size larger engine 28hp+ would be more suitable.
I work on a lot of boats, Cats and monos. The FP 38' is one of the easiest to work on with ease of access and space to all major components. Removing the fuel tank for cleaning was a 45 minute job. Re-installing the fuel tank the same. Extra race ways and under filled race ways for wiring makes adding electrical equipment a breeze.
Roberts are good boats. But once you experience the difference between a 36' Roberts and a 36'-38' Cat you'll see why Cats have become more popular.
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Old 09-06-2010, 06:05   #4
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The principal performance parameters in a multihull are: Weight, beam-waterline to length ratio, sail area. All else equal a longer boat will be faster.

As for planning your passage times: It is a sailboat. Decide "speed floor" at which you will turn on the engines if you go slower. For many people the speed floor rises as your cruising speed under power increases.

For us; our boat cruises at about 7-8k under power so our speed floor under sail is about 4 or 5, or might be even higher if we're trying to make port on a schedule to beat darkness or weather. With a favorable wind we can sail in "the teens", but because we can't count on that our "planning speed" is 5 knots. We prefer to sail when we can.

IMHO - You should keep your planning speed slow if you want to enjoy the journey in a sailboat. That takes the pressure off and lets you sail more. Also you need to allow breaks for bad weather.
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Old 09-06-2010, 06:17   #5
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Cats have a higher hull speed than monos for a given waterline length because they have much higher length-to-beam ratio (beam of one hull at the water line).

In a nutshell, they are considerably faster than a mono of similar length and sail area, but provided that they are not too heavy or overloaded. They are more sensitive to weight than monos.

They do not go to weather as well as a good mono (fin keel, modern underbody) because they don't have keels and make more leeway. This does not apply in comparison with long-keel or bilge-keel monos.

For the same reason they are shallower draft than comparable monos and so are great for lagoon-crawling in the Carib.

Two engines have huge advantages -- redundancy, and maneuverability.

The rest is down to taste, and I guess I don't need to mention that THIS issue is highly polarizing. It seems that people either love 'em or hate 'em. It's a bit like being a cat person (so to speak), or a dog person.
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Old 09-06-2010, 06:53   #6
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Old 09-06-2010, 09:12   #7
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Sailing and motoring speed


The Fountaine Pajot Mahe 36 when sailing will normally reached speeds of about 55% of the true windspeed with just the main and Jib.

With Volvo Penta D1-30 HP engines it allows you to motor with just one engine running 2,200 RPM at 7.5 knots or 2,500 RPM at 8 knots. The engine max. is 3300rpm. You will put less hours on each engine and use less fuel by using one engine. In a 6 month season I only put 50 hours on each engine using this one engine method and the autopilot does all the driving for us. Two engines are only used for docking.

The 3 bladed folding props are 17" Dia. X 12" Pitch Left Hand (Counter Clockwise)
These 3 folding blades have less vibration than 2 bladed props and the folding allows you to run on one engine without the drag of the other static prop.

Max speed is somewhere between 9-10 knots with both engines at full throttle

The D1-30 engines are nice in the respect that you have the extra power if you need it and you can run fast on one engine and save fuel.

When you hit 9-10 knots Hull Speed, that is your limiting factor for a 36 foot catamaran.
She will go faster of course in a current or surfing condition.

I have plenty of power to spare but am limited by Hull Speed.
The only way to go faster than displacement Hull Speed is to buy a longer boat.

The Mahe 36 owners that have Volvo Penta D1-20 engines state that they run at 2000 rpm using one engine, or 1700 rpm using two engines. The Mahe 36 with D1-20 engines will do 5 knots (2 * 20 HP). At 1700 rpm on one engine she will do 4.5 knots.

To me Engines purchases are like anchor purchases. Always go one size up. Most owners state that if they had to do it again they would have went with the larger engines. Itís really to late after the purchase.

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Old 09-06-2010, 10:21   #8
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If the cat has slender hulls there will not be the usual hull speed limit.

I have sailed my PDQ32 at 12 knots without surfing.

The Leopard 38 I used to own never hit more than about 10.5.

My Orana 44 is still an open question. In a test report they claimed to have hit 17 knots with a little surfing help but that seems extreme to me.
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Old 09-06-2010, 11:08   #9
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18-20 HP too small?

Originally Posted by svone View Post
...updating to the dark side a Catamaran, I'm looking at a 35 or 38 ft Factory built boat Fountaine Pajot...are 20hp to small I'd prefer 27-30hp am I correct in thinking that 18-20 to small?
I chartered FP Tobago 35s on three occasions--all had twin 18hp Yanmars. These were more than adequate for cruising easily at 7-8 kts, and had enough power for docking/maneuvering in all kinds of conditions.

Same experience with my boat which also has the same engines. 7 kts at 2400 rpm and less than 1 US gph fuel consumption with both running.

I can understand your desire for larger engines. Mark (Cotemar) makes me envious, as I am sure they are smoother than my 18 hp Yanmars, and the power in reserve in the Leopard/Moorings 43/4300 I chartered last year was really nice to have--but that is also a much heavier boat with more windage.

There are fewer and fewer lower priced catamarans available in the 35-38' range, so if you get a good price on a catamaran in the 35-38' range, I wouldn't walk away just because it has 18-20hp engines.

If budget allows and you are looking for a newer boat, possibly coming out of charter, the Lagoon 380 and Moorings/Leopard 3800/38 (and maybe the later FP Athena 38s) have engines in the HP range you are considering.

"People sail for fun and no one has yet convinced me that it's more fun to go slow than it is to go fast." -Dick Newick
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Old 09-06-2010, 12:20   #10
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Originally Posted by Dockhead View Post
They do not go to weather as well as a good mono (fin keel, modern underbody) because they don't have keels and make more leeway. This does not apply in comparison with long-keel or bilge-keel monos.
Multi's with effective underwater foils will be faster upwind in terms of VMG when powered up than monohulls built for similar service. The often made assertion that multis can't go to weather is simply wrong.

In multis waterline length matters both to help with payload and also to reduce wave drag. All else (even length to weight) being equal the longer multi will have a higher sustainable top speed and higher average speed.

You can get an idea of relative multihull performance with the Kelsall-Shuttleworth number. Notice that waterline length is in the numerator and weighted equally with sail area.

KSP = 0.5 * (SA x DWL / Displ.)^0.5

SA = Sail Area in Sq. ft.
DWL = waterline lenght in ft.
Displ = Displacement in lbs.

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Old 09-06-2010, 14:36   #11
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I own a FP 40 (Lavezzi), with two Volvo Penta 30Hp each. Sailing is easy (easy handling), in the region where i am currently (Brazil, southeast) i also use the 5 knots bottom... to reach that speed i would need aprox 10-12 knots of wind...But, if you like sailing, you should not be in a hurry... I am learning: if i wanted to go fast on the water id buy myself one of those noisy, diesel slurping speed boats... I dont like that, so i put the sails up as soon as i can and see what happens... If i do need the power, then the size of the engines is good and with abt 2100 rpm i do abt 7 knots...

Best rgds
Pieter Kommerij
SV Onda Boa - Angra dos Reis Brazil

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