PB vs trawler

[jefndeb]

Well I sold my sailboat last year and bought 2006 Mainship 400 Trawler. We go about 8 knots putzing along and so far its been a great choice....


Jeff

[CaptTom]

For the record, my semi-displacement "trawler" has soft chines and rolls a lot.

Don't assume all the points presented as possible negatives apply to all boats of a given class, or that they're significant enough to be show-stoppers.

There are a lot of very seaworthy semi-displacement boats out there, and a surprising number of planing hulls perform quite well in seas, too.

One point which you might consider is that many of the faster and more "stylish" boats are designed to always be on shore or generator power; all electric galley, few opening windows, hatches or ports so air conditioning is needed full time, etc. They may also have much shorter range (smaller tanks, higher fuel burn.)

Conversely, many so-called trawlers, full displacement or not, are designed more for cruising, with large tanks, thrifty engines, propane in the galley, large windows and hatches to catch the breeze, etc.

I've run all kinds, and although my own current boat is always run at around hull speed, I sometimes miss the ability to "get up and go" when needed. Not enough to pay for it, but it's a good option to have.

[mvweebles]

"There are a lot of very seaworthy semi-displacement boats out there, and a surprising number of planing hulls perform quite well in seas, too."

By far, the most common recreational boat to pass through the Panama Canal is a sport fisher, an undisputed planing hull. They take a breathtaking amount of diesel, but are made to take blue-water over their bow.

Returning to topic of cruising sailboats, 40-years ago, the ultimate cruising sailboat was something along the lines of a Westsail 32 - slow, austere, and bulletproof. That's changed - Steve Dashew popularized the concept of speed having a dominant seat at the table when selecting a cruising boat.

My final point to the OP - although this is off-topic for a sailboat forum, I applaud you for getting down to what you really need and setting aside the marketing hype. There are some fine vessels out there that are not trawlers, but will get it done. And frankly, there are some seaworthy-looking trawlers that are not nearly as beefy as they look. Can't judge a book by its cover.

[ranger58sb]

Originally Posted by Karlvr

I’d 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. I’m in no hurry to get anywhere when I’m out so I don’t need to get up on plane and go, I just want to putz along. Any problems with cruising a power yacht at trawler speeds?

Ref thread title: a trawler is a PB.



In general, as long as you run diesels at the correct operating temps, slow speeds can be fine. Many recommend occasional periodic higher RPMs (and load) to blow out aftercoolers and turbos... but also in general, engine longevity is a function of how much fuel it burns in its lifetime... and lower RPMs = less fuel = longer life. More info on boatdiesel.com and trawlerforum.com (latter is a sister site to CF).

Some hulls are less comfortable at some low speeds in some sea states. It almost doesn't matter whether the hull form is full, semi-displacement/semi-planing, or planing... seems more to be about individual instances of hull shape. Many full displacement trawlers roll -- a lot! -- at their slow speeds. (Hence why stabilizers of various types are not completely uncommon.) And most of the other hull forms have their strengths and weaknesses, too. (And hence why stabilizers, etc etc etc)

Many "trawlers" these days have pretty much the same hull form, or very similar to many of the motor yachts: semi-displacement/semi-planing. Most of the difference about those kinds of "trawlers" tends to be about deck and house styling, etc. See Grand Banks for example, compared to one older Hatteras LRC.

Ref the comments about wandering: Can be sort of true, easily fixed. Autopilot.

Comments about planing hulls plowing at low speeds: Generally, wrong... but that might have depended on what the poster meant by slow. At theoretical maximum hull speed (same formula used by sailboats and trawlers and so forth), most planing hulls are not plowing. Even better fuel economy happens at about 1 knot less than that (1* SQRT(LWL)) instead of 1.34*. Plowing will indeed start happening once a semi- or planing hulls starts trying to climb it's bow wave. Full or semi displacement trawler, motor yacht, whatever... matters not.

-Chris

[ranger58sb]

Originally Posted by mvweebles

[I][COLOR="Red"]
My final point to the OP - although this is off-topic for a sailboat forum,

Not off-topic at all... in the powerboat section of a cruising forum.

-Chris

[Group9]

Originally Posted by skipmac

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.

We had heard some of the same things when we were looking at going from sailing to power boating. We ended up getting a Bertram 42 motor yacht. It has the exact same dee vee hull that the 42 sport fish has.

We have found that those fears of excessive rolling, and not tracking well, were unfounded. It tracks so well, we don't even use the autopilot on short straight runs, and our marina has a little bit of a flaw that allows swell to come inside when the wind is from a certain direction. There is Grand Banks 36 tied up near us, and watching it roll in those inside the marina swells, as opposed to how little ours rolls, made me really glad we picked a boat with the deep V hull.

Pros. It goes through bad weather like a hot knife through butter, especially head on. We haven't found a sea it won't eat up and spit out so far (one funny incident was coming back from an air show in four to five footers and barely noticing them when my BIL pointed to our stern and laughed as there were five center consoles that it looked like we were towing that were letting us break trail for them).

Cons. You don't get anything for nothing. Fuel mileage is 2 nm per gallon at best, a knot under hull speed. Reverse that to 2 gallons per nautical mile up on plane (we max out at 16 knots) and it throws out a wake that could be considered attempted manslaughter in the wrong situation.

[Pelican_38]

I'm a fan of proper downeast boats. They are semi-displacement and are typically powered to reach cruising speeds of 13 knots through about 17 or 18 knots.

They still behave well at much lower speeds. They can certainly obtain higher speeds if you want to pay for the hardware and the fuel. For me, I'm happy with 14 knot cruise and 7 or 8 knot "slow cruise".

[Cadence]

The OP stated he was in no rush and it sounded like budget may play into his decision.
If he can hold out for a full displacement hull, his fuel cost would probably lower.

[ranger58sb]

Originally Posted by Cadence

If he can hold out for a full displacement hull, his fuel cost would probably lower.

Maybe, but fuel is often not even close to the largest powerboat expense, and differences between 2.5 NMPG and 3.5 NMPG (for example) may be trivial for many.

FWIW, we get approx 2.5 NMPG at about 7 kts (theoretically, from engine prop curves and our own speed tests)... with 900 horsepower available but loafing along...

-Chris

[Cadence]

Originally Posted by ranger42c

Maybe, but fuel is often not even close to the largest powerboat expense, and differences between 2.5 NMPG and 3.5 NMPG (for example) may be trivial for many.

FWIW, we get approx 2.5 NMPG at about 7 kts (theoretically, from engine prop curves and our own speed tests)... with 900 horsepower available but loafing along...

-Chris

You are burning 3 GPH give or take? I believe he could do considerably better
with a displacement hull. You probably get higher efficiency getting on top of the water.
He wouldn't need 900HP

[Simi 60]

Originally Posted by Cadence

You are burning 3 GPH give or take? I believe he could do considerably better

All depends on the comfort level wanted and the size vessel needed to achieve it.
As full time cruisers, we wouldn't consider anything smaller than what we have.

Our fuel burn measured over 3 years at 7.5knots has been close enough to 0.5 gallon/nm or 4gph or 15lph.
That's using around 80hp of the 350hp we have available pushing 60ft and 65 tonne through the water.

[ranger58sb]

Originally Posted by Cadence

You are burning 3 GPH give or take? I believe he could do considerably better
with a displacement hull. You probably get higher efficiency getting on top of the water.
He wouldn't need 900HP

It works out to between 3-4 GPH when we run slow. Partly because I sometimes forget -- ort get in a "hurry" -- and run the engines at 1200 RPMs (~8kts) instead of 1000 (~7 kts). But sometimes because opposing current or wind mandates sllightly higher RPMs to maintain ~7+ kts.

Indeed, with a displacement hull, much less horsepower would be more normal.

That said, how many horsepower I've got total is only a minor detail. If I'm running at ~ 7 kts I'm not using all that much HP, would be using the same HP if we had smaller engines, etc. (There's some additional overhead, of course, with our larger pistons and so forth, but it doesn't account for much.)

IOW, a displacement hull with smaller engine(s) could do better, maybe, but hard to say whether "considerably" better.

And then if I need to get somewhere more quickly, we have the 20 kt option, which wouldn't be available with a displacement horsepower and negligible HP.

Not a recommendation to use our approach, just an observation about what's feasible.

-Chris

[Cadence]

Originally Posted by Simi 60

All depends on the comfort level wanted and the size vessel needed to achieve it.
As full time cruisers, we wouldn't consider anything smaller than what we have.

Our fuel burn measured over 3 years at 7.5knots has been close enough to 0.5 gallon/nm or 4gph or 15lph.
That's using around 80hp of the 350hp we have available pushing 60ft and 65 tonne through the water.

That Kortz nozzle probably helps also. Out of curiosity, if you run at 75% or so of throttle what are the stats?

[Simi 60]

Originally Posted by Cadence

That Kortz nozzle probably helps also. Out of curiosity, if you run at 75% or so of throttle what are the stats?

Haven't done a long run to confirm the burn but 1500 rpm gets close to 10 knots and prop curve says that'd be about 40litres/hour
That gives us a:
3500nm range at 7.5 knots
1750nm range at 10knots

[Cadence]

Originally Posted by Simi 60

Haven't done a long run to confirm the burn but 1500 rpm gets close to 10 knots and prop curve says that'd be about 40litres/hour
That gives us a:
3500nm range at 7.5 knots
1750nm range at 10knots

Thanks, that's about what I figured. Economy went to hell. I'd be happy with the 7.5 knots. I would assume you have that much HP because she was a trawler in a prior life? Maybe your experience will help the OP make a decision.