How much horsepower do you need?

[Wayfarer]

Mine's another small horsepower rig. She's 44' long and a skinny 12.5' wide, and about 30,000 lbs. I have a single 85 horse engine, and cruise around 7-7.5 knots, and can get up to around 9 or 10 if there was a fire or something. It's enough for me. Honestly, not having the option to go fast has allowed me to loosen my grip on the throttles, and just sit back and relax.

 

[boatpoker]

38' Benford 38 Fantail
55hp
Toronto to Bahamas and back at 7.2knots - $1300 in fuel

 

[HiDHo]

Mine is standing room only.

 

[SteveZ]

HP Requirements

Hi Frank,

HP and fuel consumption are often misunderstood. The attached article addresses this issue and might be helpful.

Steve Zimmerman

 

[BandB]

Wifey B: I'd go with triple 2600 HP MTU's for a total of 7800 HP.

You must answer how fast you want to cruise. I want speeeeeeeed.

 

[Al]

Most well designed FD trawlers require about 3hp per ton.


Hummmmmm Willy- Assuming your statement is backed by knowledgeable marine architect, said as you have provided actuate data on many occasions, I have to ask from a point of "What"?????? My boat comes in at a weight of approx. 14,000 # (7 S, Ton). and is designed by Monk, a noted marine design/architect, who purposely designed our boat for that period of time of fuel efficiency was the driving force for economical, cost savings, hulls.
However, I don't believe the designed intent was to drive these hulls with 21 HP engines.

The original power for our boat was a 58 HP Perkins with a 3:1 gear turning 2150 RPM to achieve a hull speed of 6.9 knt. Your stated calculation may be a theoretical point as it is inconceivable that to achieve hull speed of our boat with 21 HP would require some formula of gears/wheels that escapes my desire to compute.
Could you extend your remarks to encompass the 21 HP potential?? Is the 21 HP a theoretical result, or is it a reality?

Thanks,

 

[dhays]

Our 36ft LWL 16ft beam 50,000lb boat has a whopping 108hp (2x54hp) total. We can get to hull speed (~8kn) at WOT, but typically operate about a knot to a knot-and-a-half below that.

We wouldn't trade my engine room space, parts cost, or fuel consumption for a even ONE extra horsepower. Suits us just fine.

When this thread came up, the Great Harbor was the first boat I thought of. It runs great with those two Yanmar engines. The GH has just the right amount of power IMO.


My North Pacific 43 has a 380hp 5.9L Cummins. It has more power than is needed and if I had been the original owner, I would have specified a smaller engine. I don't go fast. I go slow. I have lots of potential power available that I honestly never use.

 

[KnotYet]

Most well designed FD trawlers require about 3hp per ton.


Hummmmmm Willy- Assuming your statement is backed by knowledgeable marine architect, said as you have provided actuate data on many occasions, I have to ask from a point of "What"?????? My boat comes in at a weight of approx. 14,000 # (7 S, Ton). and is designed by Monk, a noted marine design/architect, who purposely designed our boat for that period of time of fuel efficiency was the driving force for economical, cost savings, hulls.
However, I don't believe the designed intent was to drive these hulls with 21 HP engines.

The original power for our boat was a 58 HP Perkins with a 3:1 gear turning 2150 RPM to achieve a hull speed of 6.9 knt. Your stated calculation may be a theoretical point as it is inconceivable that to achieve hull speed of our boat with 21 HP would require some formula of gears/wheels that escapes my desire to compute.
Could you extend your remarks to encompass the 21 HP potential?? Is the 21 HP a theoretical result, or is it a reality?

Thanks,

It is probable that the 3 HP/ton ratio starts to break down below a certain threshold.
In the case of our previous boat the 3HP/ton was sufficient to achieve hull speed.
But it was a 30 ton boat powered by a Perkins 4-236 that was nominally 85-90 HP.

 

[Captain DJ]

We have a 60 fter ex prawn trawler weighing in at + - 65 tonne

She has a NTA855M cummins rated at 350hp but at our usual 7.5knot cruise speed @ 1150rpm uses around 100hp of it.

Our 55ft "sister from another father" ship , re purposed alongside ours at the same time had a 6lxb Gardner rated at 127 hp installed.
I recon she'd be running pretty hard vs us at a fast idle.

I do not think that Gardner will be running any harder than the Cummins. The Gardner rating is a beast https://www.gardnermarine.com/wp-content/uploads/2015/05/6lxb-1.pdf and that Cummins is a great engine also.
https://www.cummins.com/engines/n855

 

[AusCan]

My full displacement hull seems will reach hull speed using just over 20hp at 1800rpm. This equates to about 3hp/ton. I am a bit overpowered with 42hp.

I may use up to about 30hp if I'm pushing a head wind with a dirty bottom.
The other 12hp has never been used.

 

[MarkW]

That is a nice looking engine room..

 

[Southern Boater]

We have a 60 fter ex prawn trawler weighing in at + - 65 tonne

She has a NTA855M cummins rated at 350hp but at our usual 7.5knot cruise speed @ 1150rpm uses around 100hp of it.

Our 55ft "sister from another father" ship , re purposed alongside ours at the same time had a 6lxb Gardner rated at 127 hp installed.
I recon she'd be running pretty hard vs us at a fast idle.

To be fair to the Gardner, their horsepower is rated in "draft" horses, as they say

 

[Art]

1977 34' Tollycraft / planing hull / Twin Mercruisers, 255 hp each / Clean bottom

4.5 to 5 knots using one engine = just below 3 nmpg

6.5 to 7 knots [7.58 knots is calced hull speed] using both engines = 2 +/- nmpg

16 to 17 knots = 1 nmpg

WOT = OMG nmpg!

I strongly recommend you fully read the link on post # 34

 

[Southern Boater]

That is a nice looking engine room..

Impressive indeed.
The only thing that lets it down is the vertically mounted paper towel.....now if that was horizontal.....

 

[Wayfarer]

Wifey B: I'd go with triple 2600 HP MTU's for a total of 7800 HP.

You must answer how fast you want to cruise. I want speeeeeeeed.

That's 50 percent more than I have at work... lol

 

[O C Diver]

I use 40 HP to push my boat at 7 knots. While the 135 HP is far more than I need, cruising at 1,500 RPM is smooth and almost quiet. For consumption perspective, with full tanks (660 gallons), I can cruising from Crisfield MD (on the Chesapeake Bay) to Fort Myers, Fl......and all the way back without fueling.

Ted

 

[markrkrebs]

Defever will hit hull speed easy

We're in the early planning stages of selling our boat on the lake and buying a boat on the southeast coast. As I'm looking at boats for sale to get myself educated on options, I'm leaning towards a trawler.

The thing that I can't figure out is the wide range of power for similar size boats. I'm scratching my head a bit at how some of these boats would even move in a headwind. So I'm clearly misunderstanding something and hoping someone can set me straight.

For reference, my current boat is 38 feet, 27,000 pounds, and has two 420 hp MerCruiser gasoline engines. It's a planing hull and can go pretty fast if I want to burn some fuel. But, I don't normally cruise at more than 8 to 10 kts.

As I'm looking at trawlers, I see some with similar size (diesel) engines to my current boat. For example, a Grand Banks Europa 42, 43,000 pounds, with two 420 hp Caterpillar engines. On the other end of the spectrum is a DeFever (49) weighing 54,000 pounds with two 150 hp John Deere engines. Or, a Selene 40 weighing 40,000 pounds with one 300 hp John Deere engine.

Are the lower powered boats intended to run at no more than hull speed? Still hard to imagine that 300 hp can get a 54,000 pound boat even to hull speed, but obviously it must. Can't imagine being in a current or wind with that little power...snip....

My defever 49 had twin Lehman 125 horse diesel. At 1600 RPM it did 8.3 knots on 2.3 gallons per hour each, 84 total shp.after that, power is cubic with speed.

 

[Jay N]

Eric said: "I just read a post elsewhere about an 85 X 20’ boat displacing 320,000lbs powered by a 330hp Cat. 3-1 red. W 58” dia prop. This computes to less than 1/2hp per ton. She probably cruises w about 180hp applied.

My 30’ Willard has 37hp and 4hp per ton displacing 8 tons.

That 85’ boat has the lowest amount of power per ton of any boat that I know of."

Needed horsepower is, of course, directly related to performance expectations.

What if I said that I have operated a boat that is 45.7' long, 6.8' wide, draws 2.6' and displaces 18.6 tons. Oh, and it has about 2 HP! That's about 9 tons per HP!

Ok, it isn't a cruiser, but a 1:25 scale model of a 255000 dwt tanker with 32000 SHP. The relationship between weight and horsepower is typical of large vessels with high bulk coefficients. In the actual full-size vessel, it operates very happily (and economically) at a speed/length ratio of around .4 (13.5 kts) when fully loaded.

Sorry about the thread drift.

Jay

 

[nanna]

I have always illustrated the different power requirements like this:
A displacement boat- you can move it by pushing it with your body, it doesn't require very much power at all.NOW, try to lift it up out of the water(as you do when planing- That requires a heck of a lot more power!

 

[menzies]

Interesting comments on the higher cruising RPMs of some of these smaller engines. I know the answer is torque, torque, torque, but my 174hp engines WOT is 2400 and in normal conditions (neither with or against a current or big wind) I cruise at 1750 giving 8-9 knots and I have a 50 ton boat.

 

[Pete Meisinger]

If you want to go trawler speed, about 50 to 90 hp will do the job. Honest!!

But as the experts say, "Speed costs money, How fast do you want to go?"

With the exception of sailboats, I would guess that 99% of the boats on the water are WAY overpowered.

pete

 

[rgano]

As I'm looking at trawlers, I see some with similar size (diesel) engines to my current boat. For example, a Grand Banks Europa 42, 43,000 pounds, with two 420 hp Caterpillar engines.

I'm also surprised at how many single engine trawlers there are. With one engine and no thrusters, how the heck do you dock? I'm spoiled now with twin engines and both bow and stern thrusters. I just finished a charter in Florida with twin engines and a bow thruster which I thought was a common configuration. But that's not what I'm seeing now as I look at what's out there.

Appreciate any thoughts.

My GB42 Classic, essentially the same hull/weight as that 42 Europa you mentioned had twin Ford-Lehman 120 HP NATURALLY ASPIRATED engines which could drive the boat a knot or two above hull speed of 8.6 Knots, but throttle down to 1600 RPM and producing what?, maybe 50 HP each purred along at 8.4 knots quietly and efficiently. I once saw a GB, obviously with huge engines, skimming across the bay here on plane, and it just looked WRONG. A twin engine trawler with a bow thruster is not common and in my opinion is sissified, and a stern thruster?!!! Why?

Now for my little light Mainship with single engine and tiny rudder, a BT is almost essential. I think Dixiecup in reference to handling in close was mentioned - mine blows around like one at a mere 12,000 pounds.

 

[twoflew]

G'Day Frank... I've owned my 38' Europa trawler for over 8 years. It has a 2002 235hp single turbo diesel, 26,000 lbs with both bow and stern thrusters. It will cruise at 7-8 kts in most weather. The only problem I encounter is high seas here on Chesapeake Bay then I must slow down. I only burn 2 to 2.5 gph so quite economical. Good boats are out there so keep looking. (mine is for sale so send me an email to: twoflew@gmail.com and I'll give you more of my perspective. Cheers, John

 

[Art]

If you want to go trawler speed, about 50 to 90 hp will do the job. Honest!!

But as the experts say, "Speed costs money, How fast do you want to go?"

With the exception of sailboats, I would guess that 99% of the boats on the water are WAY overpowered.

pete

Hi Pete

99% is a BIG # to say that basically all boats on the water are overpowered.

Large %age of displacement hulls are possibly overpowered.

However... it is fairly difficult to actually over power a good planing hull. Saying that... I admit... speed does cost $$$. As you mention... "How fast do you want to go?"

Our 34' Tollycraft tri cabin lopes along real nice [fairly economically (2 nmpg)] at 6.5 to 7 knots [slightly under its hull speed of 7.58 calced knots]. And, it moves really smooth at 16 to 17 knots up on plane; at 1 nmpg... for getting there quicker.

Its 22 to 23 knot top end is used only for momentary tests, or, if need for quick evasive action arises. In 12 years I've only utilized WOT twice [for a limited time span] to avoid problems on the water.

However... if I were to be in need of getting away from unexpedly approaching bad weather the over 20 knot speed would be appreciated.

Sooo... to have the availability for speeds mentioned our Tolly has twins at 255 hp each = 510 hp total. Way over powered for below hull speed. But, correctly powered to go fairly quickly on plane - if/when desired or required.

 

[SoWhat]

If you want to go trawler speed, about 50 to 90 hp will do the job. Honest!!
But as the experts say, "Speed costs money, How fast do you want to go?"
With the exception of sailboats, I would guess that 99% of the boats on the water are WAY overpowered.
pete

How fast do you want to go or How fast can you go.

You will knock your teeth out trying to come up on plane on the average day offshore.

 

[BandB]

How fast do you want to go or How fast can you go.

You will knock your teeth out trying to come up on plane on the average day offshore.

Wifey B: Point of my earlier post was how fast one wants to go. I want to go 50 knots. Most don't.

As to your second sentence, just not true if you have adequate power and boat design for planing. We're offshore today, were two days earlier this week. Cruising today at 20 knots, earlier during week a smaller boat at 35 knots.

But dealing in power in a strictly theoretical manner is so not romantic.

 

[AKDoug]

Frank60 wrote;
“ Thanks for all of the replies. Very educational. I'm taking a way the following:

1. The lower hp engines will get even these heavy boats to run comfortably at hull speed. “

Not so.
Many or most FD boats can’t even reach hull speed. Unless they are overpowered. And the definitely don’t run/cruise at hull speed. Cruising speeds vary at about a knot BELOW hull speed. Our Willard at WOT probably attains hull speed but I’m not sure. Don’t have any reason to know. Other than for testing the propulsion system we never run at hull speed or nearly so. We cruise almost always at 2300rpm and a bit over 6 knots. Rated power comes in at 3000tpm for our Mitsubishi S4L2. Hull speed for our 30’ Willard is 7 knots. Unobtainium basically.

Most all FD boats run about exactly the same speeds .. relatively speaking. It the nature of the hydrodynamics involved. If somebody says their FD trawler runs at hull speed and it’s true, they have a SD hull form .. as almost all trawlers do.

I cruise at 7 knots at 2650 rpms with my Yanmar 4JH2E, only when making open ocean crossings or running against the current. That's 70% rpms, but I normally run at 1850 and 5.5 knots which feels much more comfortable and burns only 40% of what it takes to run 7 knots. I feel overpowered since the 7 knots is hull speed, and there is still another 30% of max rpms that I never get to access since the boat doesn't want to run any faster anyway. 100% rpms get me about 8.3 knots, and I never bothered to figure the fuel consumption at max rpms.

You definitely are slower to accelerate, and throwing it into reverse doesn't have an immediate effect slowing or backing. You just don't put yourself into holes where you would need to back out or stop quickly. Since you are moving slowly (all of the time) you are much slower to get yourself into a spot and have time to avoid those situations.

I admire how fast large horsepower vessels can accelerate and back down, but would never want to trade my fuel efficiency for theirs.

 

[denverd0n]

With the exception of sailboats, I would guess that 99% of the boats on the water are WAY overpowered.

Among full displacement (or nearly so) hulls, I am sure that's right. I saw an ad for a 1973 Gulfstar 43 the other day. This is a modified version of their motorsailer, so very much a displacement hull. The seller is ever-so proud of the fact that he put twin 370hp engines in it! That's about 15 TIMES the hp it needs to reach hull speed! What a MORON!

 

[rgano]

How fast do you want to go or How fast can you go.

You will knock your teeth out trying to come up on plane on the average day offshore.

With miles and miles of bay systems hereabouts, even when I had a trawler, I spend most of my time in sheltered waters. Being sort of in between the trawler world now and the go-pretty-darned-fast guys with powerful OBs size and speed-wise, I wanna go faster than my fast cruise of 16 MPH where I use 80% of my horses. I wonder if I can swap my 315 horses here for 400?

 

[BandB]

With miles and miles of bay systems hereabouts, even when I had a trawler, I spend most of my time in sheltered waters. Being sort of in between the trawler world now and the go-pretty-darned-fast guys with powerful OBs size and speed-wise, I wanna go faster than my fast cruise of 16 MPH where I use 80% of my horses. I wonder if I can swap my 315 horses here for 400?

Wifey B: If you have more hp than needed, can always slow down, but if you have less than desired there is no slow up button.