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Old 19-10-2014, 10:15   #1
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Powering PDQ 44

Hi,
what is the maximum speed a PDQ 44 (Antares, PDQ 44 Antares catamaran: Well engineered and crafted cruising yacht) can do SAFELY if I would replace its cruising engines with more powerful engines ? By safely I mean, to avoid capsizing in an open ocean trip. And no sails being used during the trip.
And second question, what is the amount of power each engine should have ?

Thanks in advance.
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Old 19-10-2014, 10:27   #2
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Re: Powering PDQ 44

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Originally Posted by nulik View Post
Hi,
what is the maximum speed a PDQ 44 (Antares, PDQ 44 Antares catamaran: Well engineered and crafted cruising yacht) can do SAFELY if I would replace its cruising engines with more powerful engines ? By safely I mean, to avoid capsizing in an open ocean trip. And no sails being used during the trip.
And second question, what is the amount of power each engine should have ?

Thanks in advance.
Used ones are $700,000. In your other thread you said your budget was $150K so what's the point?

The A44 is a sailboat and has keels which would slow down a power boat. You don't need those on a power boat. If you want a power boat then buy one.
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Old 19-10-2014, 12:08   #3
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Re: Powering PDQ 44

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budget was $150K so what's the point?
.
it is just the example boat, I want to know how much horse power do you need to run it fast, and what is the maximum speed I would get.

If you don't know the answer, there is no need to sabotage my question.
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Old 19-10-2014, 13:27   #4
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Re: Powering PDQ 44

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Used ones are $700,000. In your other thread you said your budget was $150K so what's the point? .
I want to change the engines on the cat I will buy, and I want to put the biggest one possible , so I can run away from storm if I get caught. Security is a priority for me. I don't want a power boat, I will be buying a sail boat, that's decided already.
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Old 19-10-2014, 13:37   #5
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Re: Powering PDQ 44

I suggest you google "hull speed" as putting in the biggest engines doesn't make any sense.

I also suggest putting together a coherent set of questions and searching for the answers before posting as the threads you've recently started make you look like a troll or a fool rather than just inexperienced.
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Old 19-10-2014, 13:39   #6
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Re: Powering PDQ 44

The engines are amidship in the bilge. This is to keep the weight centered. You will have trouble with height clearance to increase the horsepower.
Most catamarans will sail much faster than they can motor unless you increase the horsepower by an extreme amount.
This will add so much weight that they will no longer sail fast and become possibly unseaworthy.
But you will have to find another model if you pursue this idea.


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Old 19-10-2014, 14:11   #7
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Re: Powering PDQ 44

Quote:
Originally Posted by nulik View Post
Hi,
what is the maximum speed a PDQ 44 (Antares, PDQ 44 Antares catamaran: Well engineered and crafted cruising yacht) can do SAFELY if I would replace its cruising engines with more powerful engines ? By safely I mean, to avoid capsizing in an open ocean trip. And no sails being used during the trip.
And second question, what is the amount of power each engine should have ?

Thanks in advance.
I'm not sure this is an easily answerable question. Perhaps the designer of the hull in question may know, but even they may not know. It may be something that would require a computer model, tank testing, or live experiments.

Capsizing is rather rare, usually from having too much sail up with too much wind and getting blown over in a storm or getting broadside to breaking waves. Under power, if were going really really fast down a wave and dug one of your hulls into the wave in front and had enough energy to lift the boat and pitchpole. But boy that would require a lot of speed (i.e. energy in the boat). You would certainly need enough power to get the hulls to plane.

As with any shape moving through the water at some point in order to get more speed, you need to add enough power to lift the boat up and out of the water - "planing mode". That's why a 40 something foot sailing cat may have 2x 30-75hp engines, but a planing boat will have 2x 300-1000hp engines.

Remember the power from sails is above the waterline so in addition to pushing the boat forward,it pushes the bows down. The force from props, is below the waterline, and will push the bows up, and sterns down. The stern squat will add more drag for most hulls designed for sailing.

Sorry if that doesn't help you. One thing you will find that illustrates this principle is that many people will use one engine when motoring long distances. You'll find that people may cruise at say 6.5 knots on one engine, under 2 engines they may get 7.3 knots. So they double horsepower and only get another 10-15% of speed. They are up against hull speed and unless you increase horsepower 5-10x to get on a plane, you are basically stuck with small increases in speed.
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Old 19-10-2014, 16:44   #8
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Re: Powering PDQ 44

Just a suggestion, that rather than get paranoid about being in a storm and trying to get big engines so you can run away from it (dubious strategy & results), why not use the great weather /wind predicting technology that is available now so you are not in the path of the storm in the first place? As has been said before regarding the best heavy weather tactic....just don't be there.

By storm I am assuming you are referring to a named storm, a cyclonic weather system? They can move VERY fast, they can change directions, they are in known latitudes at known seasons....just don't be there!

As for your garden variety short term nasty storms, frontal systems etc. If you are bluewater cruising you will meet one, or several of these as the natural part of cruising and passagemaking (depending on where you are and when, again) but so what? If you can't handle those types of rough weather, you are in the wrong game. Learn about drogues, parachute anchors, lying ahull, and other seamanship issues. Get some experience and your confidence will grow. Lots of experience here on CF with those that have been through it already
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Old 19-10-2014, 19:44   #9
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Re: Powering PDQ 44

Nulik,
Now don't take offense here, or get your feelings hurt, I am going to try and help the BEST way possible OK? Take this to heart, and if you do it you will be MILES AHEAD..

You may be a little new, green, some wild ideas, and are poking around in the dark a bit.. What will GREATLY help you in your understanding is go to a local Yacht Club and join in the races on multihulls as volunteer Crew. Most have racing twice a week, and most are willing to take on people and train them up as Crew.. Go with what ever they stick you on, it will be free or a minimal fee.. Bring some food, drink, stay and help clean up the boat, try and buy the Skipper a beer, and they will help you a lot..

Then you can be more selective move up to more of the type and size of boat you are interested in. You will learn 10 times more by doing that, by wild guessing here on this Forum. You will find most sailing people are kind and will tell you the practical answers you need. OK?

The direct answer to your question in this case is: You would not go to ridiculous sized engines. On a Cat they are best called "Diesel Auxiliaries" as a Cat will go better by sail than on engines. Even motor sailing, you could call it "sailing on motor"... Heh he.. Look, my Helia 44 has the larger engine option, I am 13 ton loaded with gear, and pretty large and I have 55 HP Volvos. I can do over 9 knots under power with NO WIND assist. Anything more would be wasted and fuel goes up exponentially over about 9 knots. Even most of the power cat sorts do not cruise much over that due to fuel economy..

Now: With a main up and any kind of wind, I am going far faster than hurricanes move for example.. I mean in trying to outrun one, I can sail safely running off the wind on the "safe semi-circle" away from a cyclone or hurricane (in the northern hemisphere) at 20+ knots in the right conditions under sail..

Now from engine engineering, much over about 55 HP is just on cost effective on a sailboat that size.. OK? Unless you have no rig at all and can only motor, but that is a different kind of boat, a power cat. You CERTAINLY would not repower to larger engines on a sailboat, without some kind of specific plan, OK?

Hope I have been a help, FOC, Helia 44
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Old 19-10-2014, 19:51   #10
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Re: Powering PDQ 44

As others have said - use google - there are dozens of articles and web pages to help calculate the HP you need.

For example:Power Catamarans Planing V. Displacement Comparison

and

http://www.multihulldesigns.com/pdf/powercatslt.pdf

and

http://www.bwseacat.com/content-25.html (lots of theory and formulas)

and

Catamaran hull speeds.

explains much of what you want to know

A friend was a captain on a 51 foot cat with 80 HP Yanmars and he motored at 10 knots with a top motor speed of 13 knots.

In 20 knots of wind he could sail at 15 knots and once made 20 knots for an extended period of time with 30 knots of wind.

You are headed off in the wrong direction if you think bigger engines are the answer to safety in a sailboat.

A very serious consideration for re-powering is prop clearance. If you double the horsepower you'll need MUCH larger props and I doubt there is enough room to swing the prop you will need.

What you want to do is pretty unlikely!
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Old 19-10-2014, 20:30   #11
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Re: Powering PDQ 44

Repowering a cruising cat to be able to do storm avoidance is likely a waste of time. The engines would very large and you would have to carry massive amounts of fuel to power those engine.

Storm avoidance is not that difficult if you pay attention to the weather. You have lots of advanced warning with named storms, and you should not find yourself in a position where you would try to out run a storm. In our circumnavigation, we never had to out run a storm, and we always had contingency plans in place so that we could be out of harms way when if a storm is heading our way. It's not that hard to do. You usually have three days warning at least, and you can do a lot in three days at normal vessel speeds.

We did use our engines for storm avoidance when sailing twice to New Zealand. Generally a low pressure area comes across the Tasman Sea about once a week. So when we went from Fiji to New Zealand, we would always leave on the back side of a Tasman low, and then motor through the following high pressure area. We would arrive in New Zealand just before the next low pressure area came through. Moving under power was very useful to get through high pressure areas, and so this was an effective storm avoidance measure. Yachts that did not turn on their engine were guaranteed to get hit by one low pressure area on the way to New Zealand because they made very few miles for three days in the high pressure area.

So the concept of using the engine for storm avoidance is a valid one in certain instances. But using engines to power a sailing catamaran at twenty knots because you are in the wrong hemisphere in hurricane season is probably poor seamanship and could be dangerous. Fuel lines clog, engines break down etc.
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Old 19-10-2014, 23:20   #12
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Re: Powering PDQ 44

I agree with all the advice about reconsidering your idea, and am certainly no expert. But, FWIW, I am reminded of a day charter trip on a large cat out of Maui that I once took. I don't remember the exact figures but the captain had delivered a similar large sailing day charter cat in Hawaii with huge engines, several hundred HP IIRC. It was able to motor at a surprisingly high speed, again a bit fuzzy, but something like 20 knots. It might have been a Kurt Hughes design and it was 60' or more in length. So it apparently can be done on a large cat designed as a sailing vessel. However the captain also said the engines were pretty quickly replaced by smaller more appropriately sized ones, though I don't remember why. I can give you no further info but if you are adept at searching I suppose you might be able to find out more about this. However, as I stated before, I do agree with all the advice given about reexamining your plan.
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Old 20-10-2014, 00:15   #13
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Re: Powering PDQ 44

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Fuel lines clog, engines break down etc.
Masts fall down, sails shred etc
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Old 20-10-2014, 01:24   #14
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Re: Powering PDQ 44

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I agree with all the advice about reconsidering your idea, and am certainly no expert. But, FWIW, I am reminded of a day charter trip on a large cat out of Maui that I once took. I don't remember the exact figures but the captain had delivered a similar large sailing day charter cat in Hawaii with huge engines, several hundred HP IIRC. It was able to motor at a surprisingly high speed, again a bit fuzzy, but something like 20 knots. It might have been a Kurt Hughes design and it was 60' or more in length. So it apparently can be done on a large cat designed as a sailing vessel. However the captain also said the engines were pretty quickly replaced by smaller more appropriately sized ones, though I don't remember why. I can give you no further info but if you are adept at searching I suppose you might be able to find out more about this. However, as I stated before, I do agree with all the advice given about reexamining your plan.
I suspect the design has been modified by kurt Hughes to a motor sailor.

Lightwave yachts in Australia has a motor sailor version of it 45 where the stern is flattened out and lengthened in the build process and fitted with 250hp engines. The Antares 44 would have to be highly and expensively modified to turn it into such a vessel and even if you had the designing naval architect involvement it may not be possible. You essentially are stuck with hull speed.

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Old 20-10-2014, 08:34   #15
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Re: Powering PDQ 44

The maximum engine size on an Antares 44 is 2x40hp Volvos due to space limitations amidships,
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