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Old 26-08-2019, 17:12   #1
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PB vs trawler

Id like to pick up a trawler but locally I am finding more power yachts in my price range. My question is about running a power yacht at slow speeds. Im in no hurry to get anywhere when Im out so I dont need to get up on plane and go, I just want to putz along. Any problems with cruising a power yacht at trawler speeds?
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Old 26-08-2019, 17:29   #2
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Re: PB vs trawler

Not a problem in general. I think it's bad to idle diesels all the time but if you run them enough to get up to hull speed should be fine. In my opinion it's a win/win. Go slow and get fuel consumption similar to a trawler but you can still go fast if you need to.
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Old 26-08-2019, 18:19   #3
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Re: PB vs trawler

No personal knowledge but in previous threads here on CF folks have opined that planing hulls don't behave well at low speeds. Things like rolling, poor tracking and poor rudder response have been mentioned.

If you don't get adequate response to your question, a search of the archives here will bring up a lot of info.

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Old 26-08-2019, 18:31   #4
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Re: PB vs trawler

That’s a good point. You’re right. I was thinking about motor problems but my brothers boat seemed to “wonder” at low speeds.

Thanks for the tip. I’ll look through the archives.
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Old 26-08-2019, 22:07   #5
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Re: PB vs trawler

There are many reasons for a "wandering" boat, many planing hulls don't behave thusly.

I find having speed is nice, speed over your typical classic trawlers speed. Today I crossed the Straight of Georgia in BC in a BackCove 33. The winds were around 20 knots and eventually built to 25 knots. We were taking the boat from Granville Island to Nanaimo.

We averaged 16 knots with a high of 23 knots. Today was not the kind of day you wanted to be out the Strait unless your boat was a larger heavy displacement sailboat, then pure joy.

Sometimes you want to get where ever "there" is. This desire may be due to weather, schedule including transiting "rapids." Sometimes you want to do the long jump quickly then slow down to enjoy the area at 7 or 8 knots.

I prefer to have a choice of slow or fast, but that is me. Many are content to enjoy the slower pace, nothing wrong with that as long as it is your thing. What I can prophesize is that if you do get a boat capable of faster speeds, you will use this option more than you might realize now.
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Old 26-08-2019, 22:39   #6
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Re: PB vs trawler

You might get more answers and more informed answer from the Trawler Forum
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Old 27-08-2019, 02:16   #7
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Re: PB vs trawler

Greetings and welcome aboard the CF, Karlvr.
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Old 27-08-2019, 09:32   #8
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Re: PB vs trawler

I've only owned one large planing power boat and it seemed to do fine at displacement speeds. No serious wandering or wallowing but then I didn't take it out in any really nasty weather.


Son in law has a 42' sport fisherman and it seems just fine at slower speeds. He's usually running 28-30 kts to get there but then he's trolling for hours and hours and has no complaints about handling.
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Old 27-08-2019, 09:36   #9
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Re: PB vs trawler

It seems to depend on where you sail. A good friend helped move a 74 foot fast cruiser from here in Newfoundland to Chesapeake Bay for the winter. Upon returning he asked my father in law what could be installed on the boat to make it better in rough weather and the old skipper responded with "a for sale sign". He had simply visited the boat prior to departure but with over fifty years as a master mariner he was well aware of the boat's limitations.
The crew normally sails a Niagara 35 and has transitted the north Atlantic more than a dozen times but was alarmed by the boats behaviour in even the most modest sea state.

Given the OP question I would ask where you plan to sail. The only fast cruisers here rarely leave the bay and are best described as fair weather sailors.
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Old 27-08-2019, 09:40   #10
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Smile Re: PB vs trawler

For 10 years my PDQ 34 with twin Yanmar diesels has served me well. This Canadian power cat was built using the best materials and we used it as a live-aboard from November to April each year. With 2 queen cabins, solar power, water maker, 2 A/C units and generator, we cruise the Keys and Bahamas for weeks at a time without having to stop at a marina. At 6 knots it gets about 6mpg. At normal cruising speed of 13 knots I get 3mpg. Top end is 16 kts and 1.5 mpg. Buy 180 gal of diesel and you can go a l-o-n-g way. 2 queen cabins and lots of space to spread out makes it perfect for the occasional guest. Only about 110 built and very few for sale. If you can find one, check it out.
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Old 27-08-2019, 09:50   #11
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Re: PB vs trawler

Quote:
Originally Posted by Karlvr View Post
Id like to pick up a trawler but locally I am finding more power yachts in my price range. My question is about running a power yacht at slow speeds. Im in no hurry to get anywhere when Im out so I dont need to get up on plane and go, I just want to putz along. Any problems with cruising a power yacht at trawler speeds?
JMHO Most hulls designed to plane are bay plows at low speed. A semi-displacement hull may be an option but from what you said you still won't get the efficiency of s true trawler Beware, a no. of boats are labeled trawler and aren't.
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Old 27-08-2019, 09:57   #12
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Re: PB vs trawler

Planning and semi-displacement motor yachts typically have a hard chine aft to allow them to get up on plane. This means they tend to have a sharp "snappy" roll at displacement (non-planning) speeds, and can be uncomfortable in sloppy seas. Trawlers on the other hand, have more of a rounded hull meaning they roll slower and easier (less snappy). They're generally also more fuel efficient at displacement speeds than a planning or semi-displacement boat. In terms of the engine, as long as the speed you're running the diesel keeps it at the proper operating temperature (~190F or so), you're not doing any harm. But, if running at displacement speed allows the temp to drop, the engine may be prone to cylinder glazing because unburned fuel can wash oil off the cylinder walls. This isn't the case with more modern electronic diesels because fuel metering is more precise at all rpm's. But for older mechanical diesels, it can lead to shortened engine life. My 6BTA5.9-M Cummins manual specifically states not to idle the engine for more than 10 min. to avoid this problem...
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Old 27-08-2019, 10:00   #13
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Re: PB vs trawler

Boats designed to plane have small rudders and will wander at low speeds. You will need to adjust the autopilot to make bigger adjustments, and use more counter-steer.

Older diesels (Detroits, Perkins, etc.) prefer to be more heavily loaded. Conventional wisdom was to run at WOT for 5-mins per hour. Newer common-rail/Tier 3 diesels are more forgiving, but an exec at one of the major engine OEMs said it didn't hurt to run-up after long periods of low-speed operation.

Semi-displacement boats such as a Grand Banks behave well at low-speed and will get-up on plane, albeit the lower end of planing (15-18 kts or so). Mileage halves at the higher speed, of course.
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Old 27-08-2019, 10:25   #14
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Re: PB vs trawler

Quote:
Originally Posted by Karlvr View Post
Id like to pick up a trawler but locally I am finding more power yachts in my price range. My question is about running a power yacht at slow speeds. Im in no hurry to get anywhere when Im out so I dont need to get up on plane and go, I just want to putz along. Any problems with cruising a power yacht at trawler speeds?

Hi Karlvr


From a hull design standpoint the things you have to give up to get good planing performance are:


1) Fuel economy at low speeds (due to higher drag from a larger wetted area and less favorable prismatic coefficient)


2) Sea-kindliness, that is, comfort in adverse sea conditions


3) Seaworthiness, that is, safety in adverse sea conditions. (But a higher speed boat can often outrun weather that a trawler must endure)


4) The wake the boat produces will be greater



Now, the extent of these tradeoffs vary among specific cabin cruisers (planing boats). In most cases, they will perform OK at trawler speeds.



In protected waters, mainly people complain about fuel economy. Most cabin cruisers (planing) in the ~30' range cruise at around 18 knots and will end up getting one to two nautical miles per gallon of fuel with only a modest improvement in fuel economy at lower speeds.


For a diesel, fuel burn is around 1 gallon per hour per 20 horsepower developed, so if you have, say, twin 160 HP diesels running at 75% power, you burn 12 gallons per hour total. For modern gasoline engines it's 1 gallon per hour per 12 horsepower, so the same boat but with gassers would burn 20 gallons per hour total.
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Old 27-08-2019, 10:28   #15
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Re: PB vs trawler

Karlvr:
From your brief description, it sounds to me like you would be best served with a true displacement hull, whether you call it a trawler or not. Besides speed, there are other differences between these various types of vessels. You should look seriously at hull characteristics in light of how you intend to use the boat, where you will be cruising, how far to your average destination, how much time can you afford to devote to a trip, etc., etc.
Where are you located?
What approximate price range are we talking about?

[bias declared - I like going slow!]
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