Overpowered Boats?

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wizard

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Joined
Nov 2, 2011
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35
Hello All,

I'm looking at trawlers, etc. for future ICW (maybe Bahamas) cruising.* I am an ernest newbie.* In trying to educate myself, and looking at fuel consumption, I am developing a real concern that my cruising ability will be limited by fuel costs.

I seems like most trawlers are over powered.* I am dismissing the "fast trawler" group.* But beyond that, it seem like most of the trawlers in the 40 foot range have 300 to 400 HP and the fuel consumption to match.

I read that diesels don't like to be run at very light loads, so throttling down, (say from 8 knots to 6 knots) while saving fuel, might hurt your engine(s) in the long run.* Is this true?

I have looked at catamarans as an alternative, but the modest-sized PDQ 34 has twin 110's and it displaces 15000 lbs.* The Great Harbor 37, at 47000 lbs uses twin 54's.* The disparity between the two doesn't make sense to me.

Are manufacturers willing to install smaller engines upon custom request?* Will doing so give rise to other problems?** Are manufacturers moving towards more fuel efficiency as fuel costs rise?

Thank you for any opinions -

Mike (wizard)
 
My tug with a 330 hp Cummins cruised at 9 knots at 1800 rpms. Two miles per gallon. My buddy's 40' Pilgrim with a 100 hp Westerbeke curised at 6 knots and got better milage than we did.
The difference is that 9 knots will get you somewhere in a day where 6 knots may not.


-- Edited by Doc on Friday 25th of November 2011 07:04:34 PM
 
Are you shopping for new boats only? There are a ton of older boats with smaller motors that get fabulous gph.
 
wizard wrote:
Hello All,

I'm looking at trawlers, etc. for future ICW (maybe Bahamas) cruising.* I am an ernest newbie.* In trying to educate myself, and looking at fuel consumption, I am developing a real concern that my cruising ability will be limited by fuel costs.

I seems like most trawlers are over powered.* I am dismissing the "fast trawler" group.* But beyond that, it seem like most of the trawlers in the 40 foot range have 300 to 400 HP and the fuel consumption to match.

I read that diesels don't like to be run at very light loads, so throttling down, (say from 8 knots to 6 knots) while saving fuel, might hurt your engine(s) in the long run.* Is this true?

I have looked at catamarans as an alternative, but the modest-sized PDQ 34 has twin 110's and it displaces 15000 lbs.* The Great Harbor 37, at 47000 lbs uses twin 54's.* The disparity between the two doesn't make sense to me.

Are manufacturers willing to install smaller engines upon custom request?* Will doing so give rise to other problems?** Are manufacturers moving towards more fuel efficiency as fuel costs rise?

Thank you for any opinions -

Mike (wizard)
*

The following operating parameters are for*my single screw semi-displacement 37 footer (around 28000 lbs, 34.7' w/l),*and may be compared to other similar vessels.* Overpowered at 210HP?* Yes, but not nearly as overpowered as other similar boats.* In addition, you need to remember that boats need to be overpowered a certain amount to accomodate for rough water where strains on the engine require additional horsepower.

This boat probably only needs around 100HP or so to adequately accomodate the above, but the 210HP engine is so lightly turboed, that it acts more like a naturally aspirated 130HP version of the same engine.* And it is operated at 50% of the*horsepower rating for about 5% of the time to give the engine the work it needs.* No repairs or maintenance effects have been noticed after 4500 hours.

Also, many modern higher horsepower semi-displacement boats have engines needed to drive them to planing speeds allow operators to "come back to safe harbor before being caught out in a storm".* This phrase has been known to sell quite a few boats, but in practice, it is considerably less important that the weight given to it in the sales effort, and has resulted in similar hulls being equipped with 300-400 HP, or more.*

The ability to operate high horsepower engines at very low outputs without damage is thought to be possible, but may be engine/operation dependent.* This particular topic has generated a large amount of discussion on many boat blogs/forums, and there is a considerable amount of information about it*on boatdiesel.com**

In addition, you need to look at boats designed specifcally for your intended use.* Low (or high)*powered boats designed for inland river/lake service is not what you need to be looking at if you intend any coastal/occasional ocean service.

Hope the following is helpful:

*

Really Slow Economy cruise:** 1400 rpm, 6.1 kts, S/L 1.04, 61.2% propeller efficiency, 26 hp (12% of ME rating), 1.6 gph, 3.8 nm/g, 175 FE coolant temp, 380 FE pyro, 1.0 lb turbo boost, 206 operating hours with a range of 1257 miles (90%).

Slow Economy cruise:** 1500 rpm, 6.4 kts, S/L 1.10, 60.5% propeller efficiency, 32 hp (15% of ME rating), 2.0 gph, 3.2 nm/g, 175 FE coolant temp, 420 FE pyro, 1.5 lbs turbo boost, 165 operating hours with a range of 1056 miles (90%).

Fast Economy cruise:** 1600 rpm, 6.8 kts, S/L 1.16, 59.7% propeller efficiency, 39 hp (19% of ME rating), 2.4 gph, 2.8 nm/g, 178 FE coolant temp, 450 FE pyro, 2.0 lbs turbo boost, 138 operating hours with a range of 935 miles (90%).

Slow Fast cruise:** 1700 rpm, 7.1 kts, S/L 1.21, 58.8% propeller efficiency, 46 hp (22% of ME rating), 2.8 gph, 2.5 nm/g, 180 FE coolant temp, 480 FE pyro, 2.5 lbs turbo boost, 118 operating hours with a range of 838 miles (90%).

Fast cruise:* 1800 rpm, 7.4 kts, S/L 1.27, 57.8% propeller efficiency, 55 hp (26% of ME rating), 3.4 gph, 2.2 nm/g, 180 FE coolant temp, 510 FE pyro, 3.3 lbs turbo boost, 97 operating hours with a range of 718 miles (90%).*

Really Fast cruise:* 2000 rpm, 7.9 kts, S/L 1.35, 56.0% propeller efficiency, 74 hp (35% of ME rating), 4.5 gph, 1.8 nm/g, 182 FE coolant temp, 570 FE pyro, 5.1 lbs turbo boost, 73 operating hours with a range of 579 miles (90%).
 
The*JD 4045D produces about 80 horsepower.* It's able to push the 14-ton Coot about 2/10ths of a knot faster than hull speed, absent waves and wind.* So, I consider the engine pretty well matched with*the boat.* 2200 RPM gives me hull speed of about 7.5 knots; 1000 RPM*close to*4.5 knots.
 
Willy (see avatar) is a fairly efficient boat of 8 tons driven by a 40hp Mitsubishi engine w a 18X14 prop. We cruise at 6.15 knots at a gallon an hour. We run the engine 2300 rpm at cruise (3000 rpm engine) w very low noise and vibration. At 5 hp per ton Willy's a bit over powered for a full disp hull and would be more economical if the hull shape were cleaned up some and the 2 tons of ballast removed but Willy's mission in life (37 yrs) is more toward a comfortable boat w an easy motion and excellent seaworthiness than economy.*
 
Jay N has given a good look at a very nicely setup boat .

Sure another few fractions on fuel burn could be gained with a smaller engine working harder , but the price would be higher RPM at all times (to sound dampen) and less goodie ability should he use a 200+ alternator plus inverter as "cruise generator) or add a water maker or scuba compressor, or hyd setup for stabilizers , windlass or Hyd cruise generator.

What saves the day for him is the positive boost at even really slow cruise.

A turbo boat cruised with no positive boost is a poor setup.
 
RPM is not evil. Smaller engines make less noise because they are smaller and the noise they do make (higher frequency) is much easier to isolate. Lower frequency vibrations shake boats much more easily and are much harder to isolate w soft engine mounts. Jay has done well indeed but if he was to increase his efficiency more to any degree both a smaller engine and a good full displacement hull would be in order. However at the speed I travel w Willy (6.15k) Jay dos'nt burn twice as much fuel my Willard. Having the space and stability of his big comfortable boat I'm sure most here on the forum would choose his boat over mine but I can slow down 1/2 a knot and burn far less than 1 gph but when I choose my boat I went overboard on fuel economy. Now I think there are much more important things than fuel economy. But if the economy gets much worse my 1 gph boat may become my only ticket to boating w a trawler the way I like it.
 
nomadwilly wrote:Now I think there are much more important things than fuel economy. But if the economy gets much worse my 1 gph boat may become my only ticket to boating w a trawler the way I like it.
*True enough....If the economy gets to the point that a fuel burn of 1gph keeps a lot of folks off the water, there will be far worse consequences than losing your water activities. A real good start to preclude this from happening is November of next year.
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-- Edited by SeaHorse II on Saturday 26th of November 2011 12:40:36 PM
 
Hi All,
Thank you for your kind and thoughtful replies. Jay, particularly yours.
I am primarily considering used boats, but I used the currrent PDQ and the Great Harbor as examples.
As to used, most were designed and engined in an era of lower fuel costs. So when Tom states that there are lots of used boats that get "fabulous gph", I know about the Manatee with 85 HP, but what others come to mind?

Mike
 
There is a whole thread about what burn rates people are getting on their boats. For instance, I have a 35' 1986 vintage CHB make boat with a single 130-ish HP Perkins motor that gets 1.666 GPH. Nothing overpowered about that.
 
wizard wrote:
Hi All,
Thank you for your kind and thoughtful replies. Jay, particularly yours.
I am primarily considering used boats, but I used the currrent PDQ and the Great Harbor as examples.
As to used, most were designed and engined in an era of lower fuel costs. So when Tom states that there are lots of used boats that get "fabulous gph", I know about the Manatee with 85 HP, but what others come to mind?

Mike
*Prairie 29 & Atlantic Prairie (Jack Hargrave design). *You can buy them for next to nothing now and do this:*
and have yourself a first class ride.
 
Overpowered does not necessarily mean poor fuel efficiency or anything else "bad" except that you can get up some speed if you want it.

I have a 47' Bayliner pilot house. Twin 330 Cummins.

At a 1100 rpm slow cruise *the boat makes 7 knots and gets right at 2 NMPG economy.

At a 2400 RPM fast cruise we make 15 knots and get .7 NMPG.
 
Kevin,

I love those Bayliner PH boats. We buddy boated w one a few years back. Never seen a PH so grand and inviting. Just loved the boat but it could only be a dock queen in my hands. Relative to justifying the design I'd say you'd need to do a lot of over 10 knot cruising. And if you usually run fast (12 to 14 knots) I think you've got a really excellent boat. However if it were mine and I found myself going 7 knots most of the time I'd be shopping for a 7 knot boat. The idea that one needs to have speed available for occasional*use is a bad idea for a number of reasons and it puts you in a motorsailer scenario so to speak. You don't have a good boat to do either deed and the perceived need for the go fast go slow boat has a higher price than you should pay. I think the need for occasion speed is mostly imaginary. And I'm well aware almost nobody agrees w me here on TF. No problem *...I've got a single speed boat and glad I do. But if I had lots more money I'd have a little bigger boat that ran 12 to 14 knots. And it would have a hull optimized for that speed. It would go slower very well but not perfectly but it would not go 20 knots well and never 25+. Basically a one speed boat.*
 
Hey Eric

Thanks for the compliment!

Actually the 4788 is an excellent 7 knot boat. No issues at all. Many owners drive them at 7 knots for coastal cruising all over. They*are a nice stable platform. Very comfortable. I have 800 +*NM of range at 7 knots. Whats wrong with that?

The great thing is that if you for example have limited time on your hands and want to get to a certain place, you can also cruise comfortably at 15 knots.

I'm not sure about your comment that you don't have a good boat to do either (fast or slow cruise).

Granted the 4788 is no Nordhavn, but its not designed to be a ocean crossing passagemaker. Its a coastal cruiser, entirely suited to decent weather cruising anywhere you might want to go.

Except for ocean crossing capability I don't see any advantage to being limited to displacement speeds. Yes, there are* better rough weather boats. Then again I'm not inclined to go out in snotty weather. I'd just as soon stay anchored up in a nice cove somewhere with a good book and a bottle of good wine.

When the waves die down we'll venture out and have a good comfortable journey.

I'll be taking mine on a 1500NM + trip in four months. Anacortes Washington to Seward Alaska. This will be our second Gulf Of Alaska crossing.

I*would have no issues taking this boat anywhere coastal, so long as I could pick and choose my weather windows. For example we might someday cruise the caribbean. It would be quite comfortable for that type of adventure.



And... when you talk about dock queens, that has zero to do with the boat and everything to do with the owner. The reality is that most boat owners are just too busy making a living to have the time they want to enjoy their boats. I've seen just as many "salty" dock queens as "party cruisers".

Fortunately we're not in the dock queen catergory. Our only limiting factor is the relativly short Alaska summer. Our season is April-early October then its back to ice and snow.


-- Edited by ksanders on Sunday 27th of November 2011 01:39:41 AM
 
ksanders wrote:
The great thing is that if you for example have limited time on your hands and want to get to a certain place, you can also cruise comfortably at 15 knots.

Except for ocean crossing capability I don't see any advantage to being limited to displacement speeds.

_____________________________________________________

The above statements coincide with my own philosophy.

My best friend had a 4588 and was a live a board. At first, knowing absolutely nothing about Bayliners, I was not a fan of his boat but after several short, open water cruises, I became a big fan. My brother, who had a 59' Defever, was also anti Bayliner until he visited me and saw my buddy's boat. I'll never forget his first comment after touring the boat...."You know, Walt...this is a hell of a boat!"

*
 
ksanders wrote:

The great thing is that if you for example have limited time on your hands and want to get to a certain place, you can also cruise comfortably at 15 knots.

Except for ocean crossing capability I don't see any advantage to being limited to displacement speeds.*

Ultimate fuel economy is the other possibility...most of us are willing to*forego ultimate economy*to the point where we have enough speed and*room (within cost parameters)*to meet our requirements.

Without going back to sail of course!!
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-- Edited by psneeld on Sunday 27th of November 2011 09:04:13 AM


-- Edited by psneeld on Sunday 27th of November 2011 09:08:11 AM
 
ksanders,

I'm just say'in when you go 7 knots a full displacement Krogen or similar boat would be better but then you would'nt have the 15 knot capability. So it's just a matter of how important the dual speed feature is to you. Nordic Tug even advertises "Go Fast Go Slow" and they should have a good idea how many people are seriously drawn to that feature. Kevin, do you know the boat "Jericho"? That's the Bayliner I was talking about earlier. That funny * ...I remember the boat's name and not the skipper's. Hmmmmm

By the way I do'nt consider your Bayliner overpowered.


-- Edited by nomadwilly on Sunday 27th of November 2011 02:22:32 PM
 
nomadwilly wrote:
ksanders,

I'm just say'in when you go 7 knots a full displacement Krogen or similar boat would be better but then you would'nt have the 15 knot capability. So it's just a matter of how important the dual speed feature is to you. Nordic Tug even advertises "Go Fast Go Slow" and they should have a good idea how many people are seriously drawn to that feature. Kevin, do you know the boat "Jericho"? That's the Bayliner I was talking about earlier. That funny * ...I remember the boat's name and not the skipper's. Hmmmmm

By the way I do'nt consider your Bayliner overpowered.



-- Edited by nomadwilly on Sunday 27th of November 2011 02:22:32 PM
*Agreed.

For us the dual speed thing was extremely important to the missus, not so much for me. She wanted the ability to get there quickly. Coming from a 27 knot boat before I can understand her thinking.

I on the other hand was ready to slow down in life and cruise at 7 knots. Boats I was looking at were the 49 Defever, 48 Hatteras LRC, 46 Nordhavn, even the 42 Krogen and the 40 Willard.

She was*firm about the faster cruise requirement. It became a deal breaker, and the subject of several*heated discussions. To her benefit she even read Voyaging Under Power to get more knowledgable about hull designs etc...

In the end we chose the best pilot house boat that would meet both of our cruising needs.
 
That's great ksanders that she read VUP. Do'nt know if I could get my wife to do that but she's great w everything else on the boat. One of those boats you mentioned is my all time favorite * ..Nordy 46. Wish I could go see pics of your boat and maybe even you but somebody removed the photo album sticky * ....apparently not very sticky.
 
Regardless, one needs enough power to plow through the chop.
 

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"Except for ocean crossing capability I don't see any advantage to being limited to displacement speeds."

The advantage would come from the more efficient operation at displacement speed.

Since 95% of most operation is at Trawler Crawl, giving away perhaps 30% higher fuel burn could be expensive.

-15% for poor displacement hull shape and dragging a transome,

-15% for low engine loading .

This last 15% will NOT apply to gas boats.

Admittifly getting 30% better furl burn at 3-4 gph is not big bucks , unless you travel big miles!


The light construction required for much speed may also alter the route the boat can run.

Norfolk VA to Montauk or Cape Cod might require a realy great forecast,

or its up the Chessie , down the Delaware , cost hop allong NJ , then NYC and up the LI Sound.*

Days extra.



-- Edited by FF on Monday 28th of November 2011 04:18:28 AM
 
Mark, *You do'nt need any more power to "plow through chop".

FF, * * The biggest advantage is a boat that will be much better suited to open water or rough inshore conditions and hugely more desirable on following seas. I think the fuel savings will be 35% or more. I'm against low engine loading and I'm assuming when you say "15% for low engine loading" you mean the engines basic loss of efficiency at the low load. That would vary a bit w engine type I suppose. I would think it would be more like 25% from dragging water w the planing stern and 10% for underloading inefficiency. But we're basically agreeing a 7 knot boat to go 7 knots is much better than others. Yes.
 
nomadwilly wrote:
Mark, *You do'nt need any more power to "plow through chop".
The "power margin" or power reserve designed into a well thought out boat is anywhere from 15 to 30 percent above the power needed to obtain the desired performance in calm wind and water.

"Plowing" may be elective but burning more fuel to maintain the same SOG in "chop" and wind is a reality.
 
RickB wrote:
"Plowing" may be elective but burning more fuel to maintain the same SOG in "chop" and wind is a reality.
Couldn't agree more!
 
You're talk'in fly stuff guys. I do'nt notice any loss in speed in my Willard but I suppose there is some speed loss * *....how could there not be. But it ai'nt worth talk'in about. Unless you're just look'in for something to argue about. In the 500hrs I've run Willy I've not increased rpm ever to maintain speed.
 
Rather than discuss horse power, a discussion on the hull design might be better as the hull design has a direct relationship to the horse power.* The three basic hull design are; full displacement, semi displacement and planing.* It does not take a lot of horse power for hull speed but it does take horse power for a boat to get over its bow wake and/or speeds over hull speed.* *If you know the displacement, length/beam and the hull design you probable can estimate/guess the horse power.* The hull design will also have a direct effect on the boat initial and ultra stability.**

There are some of us boat owners do not mind if the cost of fuel goes up, as our boats are fuel effient and the demand and piece for our boat will increase,k rather than decrease.*
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-- Edited by Phil Fill on Monday 28th of November 2011 12:39:19 PM
 
Lets take a typical boater who puts 150 hours per year on their boat. Loopers will do more, ICW north and south will do more but when you look at all the boats for sale, divide the number of hours on the mains by the age of the engine, on average not that many hours per boating season. Boat "A "uses 2 gph and boat "B" uses 3 gph, so one extra gallon for 150 hours, times $5 per gallon to take in some increase, give a fuel cost difference of $750.
Compared with the cost of dockage, insurance, routine maintenance, reserve for repairs, and depreciation, total fuel use should not be the deciding factor.
 
nomadwilly wrote:In the 500hrs I've run Willy I've not increased rpm ever to maintain speed.
No you didn't increase rpm but your governor increased fuel flow to maintain the rpm you selected.
 
yachtbrokerguy wrote:
Lets take a typical boater who puts 150 hours per year on their boat. Loopers will do more, ICW north and south will do more but when you look at all the boats for sale, divide the number of hours on the mains by the age of the engine, on average not that many hours per boating season. Boat "A "uses 2 gph and boat "B" uses 3 gph, so one extra gallon for 150 hours, times $5 per gallon to take in some increase, give a fuel cost difference of $750.
Compared with the cost of dockage, insurance, routine maintenance, reserve for repairs, and depreciation, total fuel use should not be the deciding factor.
*I totally agree.
 
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