Low Powered Cruiser

This boat, Yellow Cedar, shows us how much power we really need to go forth in this world of cruising power boats. Yellow Cedar looks like a retro-boat but it's not. She is 38' X 10' x (about 3') w 15000 disp, 28hp and max speed 9 knots.
See her at:
<http://www.tadroberts.ca>
At the top of the page click on "new design"
On the right side of the page click on "Yellow Cedar"
Surf the rest of the site and try not to miss "Passagemaker Light"

-- Edited by nomadwilly on Monday 21st of December 2009 12:49:27 PM

He has a great sense of style ,

and notice a proper sized engine , instead of 100hp too much!

There are still intelligent NA out there ,

AT 10 ft beam she would require a* permit , but would be easy enough to trailer.

Alaska inside passage in summer , Fl Keys or Bahamas , with a few driving days in
between?

Would work for me , tho I would probably prefer a Yanmar to a Perkins.

FF

-- Edited by FF on Monday 21st of December 2009 01:56:06 PM

Eric, you seem to favor smaller engines*using a higher proportion of their horsepower*rather than*more powerful*engines using a lower proportion.** But would there be enough*power with the "minimalist" engines under extended*high head-wind and heavy-seas conditions?* Is it true one can kill their engine "with gentleness"?

I must be permanently scarred, mentally.* On subjects such as this, the 36-year-old vision/memory of the great white shark chasing Quint's (Robert Shaw's) boat with overloaded/smoking engine comes to mind.* Trivia quetion: what was the name of Quint's boat?


-- Edited by markpierce on Friday 8th of October 2010 05:28:37 PM

markpierce wrote:.* trivia quetion: What was the name of quint's boat?

Click to expand...

orca

*

Mark,Yes. I think a diesel engine in a boat should be run at 65 to 75% load. During break in it should be run frequently at 85% for very short periods becoming longer as break in continues. A diesel engine should be warmed up slowly from chugging to 85% load in about 15 min. time or a bit more. Shut down should take less time (10 min ?).
Percentage of load is determined by fuel burn. Find out from the engine manufacturer how much fuel the engine will burn at WOT at the rpm where the engine develops it's maximum power. Insure that your boat will run at WOT at the rpm that it develops it's maximum (intermittent) power. It will be about 100 rpm shy until broken in. If it burns a maximum of 6 gph at WOT and you cruise at 2000 rpm and at that rpm you burn 4 gph you are loaded at 66% power. If you burn 3 gph it's 50% loaded ect. No one can accurately compute their fuel burn. If one takes into consideration idling through no wake zones, going slow frequently or from time to time and idling at dockside one can come close. Almost everybody burns a lot more than indicated by observing how much fuel one put's in the tank and what the hour meter says. Most engines burn about a gallon for every 20 hp for an hour. In other words if your engine burns 2.5 gph you are developing/using close to 50 hp. Is that more than you wanted to know? Needing extra power in windy conditions just dosn't happen. When it blows 40 or 50 knots and there's 5 to 7' seas I ALWAYS reduce power. My cruising rpm is 2300 and in the above conditions I always reduce engine speed to 2000. Several times I have cruised for 2 or 3 hours like this always making reasonable progress. All the above is opinion but I , of course, believe it all to be true and generally the best practice.

Thanks, Eric.* Over the slight objection of my builder some weeks ago, I*requested the installation of a fuel-rate-of-consumption meter.* He said there were other ways to accomplish this, but I want to know what's happening while I'm working the throttle.* I*like *immediate feedback.*... also,*I didn't go along with the builder's recommendation for a turbo-charged version of the*engine.* (After all, I won't be boating at 20,000 feet.)


-- Edited by markpierce on Saturday 9th of October 2010 01:28:59 AM

A flow scan has many uses , not just in checking the prop is proper , or setting cruise speeds.

The totalizer works well enough (after its set) that sticking the tank or having crap in the tank for a "fuel check" is not needed.

Best was a day in Block island , a pro fish killer boat went to fuel at Chapmans dock.

After the fill up , he read the pump meter , and asked for the owner.


He Knew what he could take on , and the meter showed more than the tank could hold.

FREE FUEL (so he kept his mouth shut) and Chapmans could screw the visitors for the entire holiday weekend.

Running the loop we did the necessary tweaking (one has to go further and further before resetting) during the trip.

It became possible to get within 1 or 2 gallon on the estimate what the 100G tank would take.

The Flow Scan ain't cheap, but its more fun (and use) than most electric toys.

Mark,If you're like me you will become less and less concerned about how much fuel you burn.
But those who burn 5 to 10 gallons an hour may differ in this priority.

"But would there be enough power with the "minimalist" engines under extended high head-wind and heavy-seas conditions?'

Ordinarily there is enough reserve power for the 40K headwinds and confused seas.

The properly powered boat WILL probably be slowed down, but sea state usually calls for a speed reduction.

Even with those $6000 Stidd seats , the coastie kids have problems with operating very long at 3+ G loadings.

For retired folks with cheap seats, bashing from wave face to wave face is a good way to overstress the boat and the crew.

MY setup in an engine rated (commercial 24/7) of 100 hp would be to shoot for 60 hp for propulsion at LRC , 80 hp for ICW or other places fuel is cheap and easy.

The sometimes extra 5% - 10% for house power , refrigeration , hydraulic needs would be OK with either cruise setup.

100% power could be carried till the fuel or crew is exhausted in heavy weather.

A CPP makes this setup really easy , and now that the prices are lower , I would certainly have it aboard.

Please enlighten the ignorant:


LRC = ??long-range cruise??

ICW = ??intercoastal waterway??

CPP = ????


Also,**is the ideal match of engine and displacement boat one with 80% power*to achieve hull speed (about 1.34 times the square root of waterline)?

Thanks!

There is no material downside to having a comfortable*power cushion*in a new install. I would size*the engine for about 50 to 60% load at hull speed in smooth water which should give you plenty of cushion for the rough water, maybe adding a cruise gen, pto for ??*etc.

My biggest fuel burn is in rough water with a following sea - about 20% to 30%more than flat water hull speed. I suggest you post this question on boatdiesel.com and use their prop calculator data. Sizing your prop to match your engine and hull is important.

I understand the desire for as low a fuel burn as practical, but this is a matter of philosophy. Fuel cost aside I feel about boats the same as I feel about floatplanes---- there's no such thing as too much power if your boat's hull configuration can take advantage of it. Obviously you can put a ridiculously powerful engine in a boat, and considerations like being able to run the engine at it's proper operating temperature have to be kept in mind.

But in twelve years of boating in the GB and the almost ten years of boating in our outboard-powered Arima before that I have NEVER heard anyone complain about having too much power in a boat. But I have heard lots of complaints from people about not having enough power, from the owners of trailer fishboats at one end of the spectrum to the owner of a Grand Banks 52 who ordered it with smaller-than-standard engines in 1998 in the interest of fuel economy and has been bemoaning his decision ever since (along with everyone who charters this particular boat).

If you have a relatively powerful engine in a boat, you don't have to use all that power (keeping in mind operating temperatures and so forth). But if you have a small engine in a boat, you can never develop any more power than that no matter how much an unanticipated situation might call for it.

Carey of this forum has a 420 hp Cat in his custom lobsterboat. For the past couple of years he's been cruising the boat at a bit over 8 knots to keep his fuel costs down, which this does quite effectively. He ensures that the temperatures are correct and he runs the engine at higher loads periodically. But should he need to--- and he has a few times that I know of--- he can run his boat at its normal cruise speed of 14-15 knots. That's a versatility I can appreciate. To be stuck-- as we are with our boat-- with an 8 or 9 knot limit is not a good situation to have in a boat to my way of thinking. We thought when we bought our GB that an 8-knot cruise would be just fine. We have since discovered--- like the owner of that way newer GB52--- that it's not.



-- Edited by Marin on Saturday 9th of October 2010 03:46:54 PM

Marin wrote:
---- there's no such thing as too much power if your boat's hull configuration can take advantage of it.

Click to expand...

Hear hear ... that just about nailed it.

Yes on the first two; CPP= Controllable pitch propeller.

Mark,Well as you can see there are many other Thoughts on how much power a trawler should have but all of them come from skippers that are familiar or intimate with semi-displacement craft. There is a very successful trawler/passagemaker that is also well known and documented. Nordhavn 46. She has 101 hp and 48000lbs disp. A top speed of 9 knots and a cruising speed of 7.4 knots (SL1.2). Maximum continuous speed of 8.7 knots w her Lugger Diesel. The Nordhavn 46 has 4.2 hp per ton. Clearly for any normal FD craft 5 hp per ton is enough power to deal with seas and wind as the Nordhavn 46 has proven the world over. The FD hull is the only hull shape that has a fixed power requirement. All other hulls can benefit from more power and to varying degrees but the hulls closest to FD can be benefit from only modest increases in power. Most trawlers need considerably more power to go at hull speed and even more to go faster yet. So at least for a FD hull 5 hp per ton is plenty of power.

nomadwilly wrote:

Mark,
Well as you can see there are many other Thoughts on how much power a trawler should have ...

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Eric, I take your comments to heart,*but am comfortable with a 6 hp/ton engine.* The only boats I've*captained have been auxiliary (inboard and outboard) sailboats, so I'm quite comfortable with cruising 6 to 7 knots.* So much so I'll have*small fore-and-aft*sails for steadying and for a two-knot-crawl-to-safety if the engine ever crashes.* Perhaps the extra windage of mast justifies the extra engine power.

*

" there's no such thing as too much power if your boat's hull configuration can take advantage of it."

Would agree in an aircraft , but sadly not for a cruiser.

If you don't mind paying for the lack of efficiency , which can be 200% to 300% higher fuel burn per hp,

and the sometimes quire shortened engine life from underloading.

Running a turboed 400hp monster at 50 hp gets very very expensive indeed.

The Oxymoronic "fast trawler" , is only for the thickest of wallets.

How Low can you GO , really depends on the marinization choice.

THe best at low power are the light truck and tractor engines, Lemans , 5.9Cummins and 3208 CATS.

Do it to a DD series 60 , or bigger industrial stock only at great peril.

FF wrote:If you don't mind paying for the lack of efficiency , which can be 200% to 300% higher fuel burn per hp,

Click to expand...

I would love to see the spec sheets on that engine.

Your "efficiency" claims seem to be based on the very small increase in BSFC at lower power but you carefully neglect to provide the information that despite the the minute loss of fuel efficiency, the fuel burn is greatly reduced.

Recreational vessels are not operated for the purpose of reducing the nation's fuel consumption. The way most of us manipulate the throttle probably burns more fuel during a voyage than the microscopic loss of fuel efficiency created by operating at lower power.

Selecting the most extreme position makes for scary reading I guess but you'll have to back up your opinion with some documentation to show things like increased maintenance costs and 2 or 3 times the fuel burn per HP at reduced power. According to that fantasy, a marine diesel engine driving a fixed pitch propeller might burn the same quantity of fuel just above idle as it does at full power.

EDIT:

Just for grins I ran the numbers on one of those monster 400 hp engines, and a Detroit just to make it a real worst case.

According to the Detroit Diesel specifications for a 6V92TA driving a well matched fixed pitch propeller, the brake specific fuel consumption (BSFC) at 425 hp is .387 pounds per horsepower hour, a pretty good figure that equates to about 23.5 US gallons per hour.

If we slow that engine down to the lowest continuous output that DD plots, and by inference, an approved operating condition, the BSFC increases to .49 lb per horsepower hour which equates to 3.5 US gallons per hour.

The increase in fuel consumption per horsepower due to lower fuel efficiency at the lower output is .014 gallons per horsepower over what it would burn if it had the same BSFC as it did at full power.

That is also equal to about .7 gallons per hour for the entire 50 hp over what the engine would burn if it had the same fuel efficiency at 50hp as it does at 425.

*


-- Edited by RickB on Sunday 10th of October 2010 09:14:29 AM

In perusing the boatdiesel site the other day I noted a*vessel doing the loop loves to cruise his*(newer) Cummins at 925 RPM for 6 knots while burning only 1.2 gph. He does open it up to 2400 RPM for short bursts. This is about 7% power draw based upon fuel consumption. Yes - ridiculous but true.

I* normally run my Perkins Sabres at about 1650 - 1750 RPM or a 20 - 25% fuel burn with no adverse issues. If I 3X the fuel burn to 2200 RPM, I gain only 50% in speed.

As noted by Marin, it is quite easy to slow down an overpowered vessel, it is called a throttle. You CANNOT speed up an underpowered vessel that is normally operating at 80% or "on the pins." Plus for very similar external engine size and not much* more cost, you can often purchase/upgrade 50 to 70% or more power to an engine for reserve.

For a new tierII/III engine I'd go Cummins or JD and quickly skip over* Yanmar and Volvo. A read of the boatdiesel archives would be informative in this regard. Would the 4 cylinder Cummins fit your space?

-- Edited by sunchaser on Sunday 10th of October 2010 10:16:07 AM

Tom,The hull won't allow you to speed up anyway so what's the point? You can't use anymore than 5 hp per ton so anything in excess of that is not only a waste but always produces an underloaded engine.


You were posting while I was. FD hulls DO NOT NEED RESERVE POWER. Most people think they need reserve power to buck head winds but in practice one needs to back off instead.*If you have a huge engine in a FD hull and want to go faster you can get 10 - 15% more speed but it hardly alters you're situation at all. The real reason you NEED more power is FEAR. You are afraid you will be lacking some day for some reason but it's not true. I have never ever needed more power and I'm right at 5 hp per ton. Fear that you're engine is prematurely wearing out. Diesel engines run at 80% loads for at least 10,000 hrs and 99% of us will never see more than a small fraction of that. Another reason people want more power is so that they can run at low engine speeds. Less noise to be sure but mostly guys just want to be more like a Harley Davidson and loaf along rather than sing along at 2 or 3 times the rpm like other motorcycles. With a smaller engine at higher revs it sounds like you're struggling to keep up and while lugging it looks and sounds like it's easy * *....like you're loafing along. So It's partly a hair on the chest thing.
But as the 46 Nordhavn shows us * * *..there is no rational need.


And as Rick points out running an engine at low revs is less efficient.


-- Edited by nomadwilly on Sunday 10th of October 2010 10:52:08 AM

nomadwilly wrote:

Tom,
The hull won't allow you to speed up anyway so what's the point? You can't use anymore than 5 hp per ton so anything in excess of that is not only a waste but always produces an underloaded engine.


You were posting while I was. FD hulls DO NOT NEED RESERVE POWER. Most people think they need reserve power to buck head winds but in practice one needs to back off instead.*If you have a huge engine in a FD hull and want to go faster you can get 10 - 15% more speed but it hardly alters you're situation at all. The real reason you NEED more power is FEAR. You are afraid you will be lacking some day for some reason but it's not true. I have never ever needed more power and I'm right at 5 hp per ton. Fear that you're engine is prematurely wearing out. Diesel engines run at 80% loads for at least 10,000 hrs and 99% of us will never see more than a small fraction of that. Another reason people want more power is so that they can run at low engine speeds. Less noise to be sure but mostly guys just want to be more like a Harley Davidson and loaf along rather than sing along at 2 or 3 times the rpm like other motorcycles. With a smaller engine at higher revs it sounds like you're struggling to keep up and while lugging it looks and sounds like it's easy * *....like you're loafing along. So It's partly a hair on the chest thing.
But as the 46 Nordhavn shows us * * *..there is no rational need.


And as Rick points out running an engine at low revs is less efficient.


-- Edited by nomadwilly on Sunday 10th of October 2010 10:52:08 AM
*

Click to expand...

Willy*i couldn't agree more in reference to displacement boats. Size your engine to hull speed or maybe 5% more.
The only application in which all the extra power really makes sense is a semi displacement/ planing hull. The only reason I don't include planing hulls is that I don't like the way they handle at slow speeds. My lobster boat (with it's long keel) handles like a dream at low speeds. However, with it's low freeboard and round chine, it's not so hot *in three to four foot seas at eight knots. It wallows and rolls a bit too much (which could probably be remedied with ballast in the keel). But, that's when the throttle goes down and we get up to full cruise.


Carey

*

nomadwilly wrote:And as Rick points out running an engine at low revs is less efficient.

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In the interest of intellectual honesty and to avoid the type of engine buffoonery posted by FF, when you quote me, please at least make a minimum effort to keep it in context.

A small recreational diesel is microscopically less fuel efficient at lower power and most operators probably use or waste more fuel by poor power management practices and bad boathandling than they would from operating at reduced power the rest of their lives.

And there are many reasons "reserve power" is useful. A fouled hull or prop, weight increases over the period of ownership, wind from most any direction and poor steering technique.

I don't think anyone is talking about doubling or tripling the HP required to move a displacement hull so the argument is right up there with angels and pinheads but I have met more boat owners who said they wish they had more power than said they had too much. They all have a throttle.

*

Rick,
I stand fully corrected on engine loading per your last post.


However I soundly disagree w you about "reserve power". *Weight increases should be taken into account at the beginning, steering should be learned and propellers should be cleaned.


Carey,



Yes but a full displacement hull should not be run at "hull speed" (as in 1.34Xthe square root of the WLL). *Hull speed can be maximum but FD boats should be run at 1.1 to 1.2 SLR * * *....not 1.34. !.34 is an expression of wave length not something to attain. I don't even know if my Willard can attain 1.34 (7 knots)







-- Edited by nomadwilly on Sunday 10th of October 2010 12:33:20 PM

The designer of the Coot, George Buehler, agrees with*Eric*about operating at 1.2 SLR:


"Id tend to cruise at about 1.2 or so speed/length ratio. 6 1/2 to 7 knots is a good clip, and the engine will easily do it. Notice the difference between 7.6 knots and 9; that translates to 1.2 gallons an hour to over 70 an hour.....

*
<center><table border="3" cellpadding="0" cellspacing="5" style="width:562px;height:223px;"><tbody><tr><td height="206" width="100%">

<center>*S/L Ratio..... Knots..... HP
1 ...... ..........5.63........ 3.9
1.1............... 6.19....... 6.0
1.2 ...............6.75....... 9.5
1.25............. 7.03...... 12.8
1.3............... 7.32...... 17.3
1.35.............. 7.6........ 23.5
1.6................ 9.0 ...... 149.3</center></td></tr></tbody></table></center>

So that's less than*9.5 horsepower for moving the 14-ton, 31.7-foot-waterline Coot on flat seas with still winds.* But that means even a 40 hp diesel is operating at only 25%.* Nevertheless, the designer specified an 85 hp engine.* I find this hard to reconcile with the recommendation to operate at 75%.* *What's up?* Inflated hp figures from engine manufacturers?* Lost horsepower at the transmission?* Or are we talking revolutions versus horsepower output where there might not be a linear relationship as in three-quarters maximum revolutions produces 25 percent of available horsepower?


-- Edited by markpierce on Sunday 10th of October 2010 01:06:54 PM

The notion of putting a big engine in a displacement boat-- by which I mean an engine capable of producing significantly more power than the hull can put to use---- makes little sense unless one just likes big engines

However I think sizing an engine at least a bit more powerful than necessary is a good idea for a displacement boat. I am of what is probably the pretty old school of engine operation adhering to what I was told years ago by one of the most respected mechanics (and pilots) in aviation (who also had and maintained himself a deFever with smaller Cat engines) who in answer to my question of what could I do to ensure long engine life said, "A piston is only going to go up and down so many times. So the easier you make life for the engine, the more times the piston will go up and down." By which he did NOT mean to run it at settings that were too low.

So if that philosophy still holds any water, I would think a somewhat more powerful engine in a displacement boat would yield a comfortable margin between running wide open all the time to achieve cruising speed and running at a more conservative throttle setting which would help keep heat down, etc. Maybe this is not true with today's generation of diesels, I don't know.

As has been noted by others, a displacement hull cannot be powered significantly faster through the water to counter a strong opposing current or to outrun an approaching front. But I think there may be times--- very rough water, for example--- where having a bit of a reserve of power might be useful. Not to go faster, just to help the boat handle the slop. But I've never run a displacement boat other than a 20-ton narrowboat in the UK where the roughest water one encounters are the wakes from the swans paddling past. So I don't know if having a reserve of power would be helpful in a displacement boat under rough conditions.

The other thing to consider is the auxiliary loads on the engine. In addition to moving the boat is it going to have to power an oversize alternator or a hydraulic pump? Is there a likelihood of significant marine growth on the bottom and/or running gear that could generate additional drag between hull-cleanings?

Plus I would imagine that selecting power for a recreational displacement boat also comes down to what's available. There are only so many marinized engines to choose from. If the hull specs on a boat indicate that 35 hp is needed to move hull-x through the water at or near its displacement speed but the only engines available near that rating that will properly fit the boat are a 30 hp and a 75 hp, which should be chosen? To my way of thinking the best choice would be the 75 hp engine.

-- Edited by Marin on Sunday 10th of October 2010 01:15:00 PM

A very*bulletproof engine in the size range you are considering*is the Cummins 4B rated at 85Hp. Trans Atalntic sells them re-conditioned with the* transmission as a package. On the west coast Seaboard marine does the same. I was just looking at the RPM and prop curves and they*look pretty good for your intended task. The 4B will go*all day at 1600 RPM burning less than 1.2 gph.

Mark,If those numbers on the Coot are accurate I'd be look'in at the Isuzu 54 hp or Yanmar 4JH at 55 hp. Then cruising at 1.34 will still set you up at less than a 50% load on the engine.
Not Ideal but better than 35 to 40%. I think I'm running my Mitsu at 60 to 65%. Seems to be a good balance between noise and under loading. 23 hp would consume about 5 quarts an hour and even w 54 hp the engine would still be under loaded. Ask George Buehler if he would recommend 54hp.

I recall chatting to the owner of Bagan, the now famous Nordhavn 57, a few years ago when he was visiting New Zealand. He had just arrived from Fiji and made the journey at an average speed of 11 kn* since it was "only 1100 miles".

Ths is an S/L of 1.5 which could only be achieved with quite a few more*hp than a "correctly sized engine" could deliver. I believe it was a Lugger 325.

Our 53 ft lobster boat with 540 hp runs happily at 9.2 Kn at only 1250 revs. I calculate this to be using 90 to 100 hp. The previous owner also did this for days at a time - interspersed with hours of idling tending nets and a mussel farm. The engine had run for 18,000 hrs before*its rebuild.**Tony Athens,**moderator on boatdiesel.com says he has yet to see an engine damaged from underloading, they just tend to last longer.

I believe there is a good case for a bit of additional hp for both displacement and semi-displacement hulls, which most of us have.

I sure like to get her up on the plane at 12 kn when the weather cuts up, she definitely handles the sea*better. It's also fun going WOT after relaunching*with new antifouling and cracking 18kn - admittedly with a knot of tide under her!*

Marin wrote:I was told years ago by one of the most respected mechanics ..."A piston is only going to go up and down so many times. So the easier you make life for the engine, the more times the piston will go up and down."

Click to expand...

Marin, you sure can find the whacko experts!

That statement not only contradicts itself, it is just flat out wrong. An engine that lasts a few thousand hours more than another one of the same because it was operated at lower power has pistons that went up and down quite a few more times its short lived higher power cousin.

If that guy had said an engine will only burn so much fuel before it wears out then he might be worth listening to. Many engine manufacturers are now listing TBO as pounds of fuel burned because that is directly related to the power produced and an engine will only produce so much power before it wears out.

He was saying this not as a literal fact having to do with how many times a piston actually goes up and down but simply as his favorite way of expressing his view that an engine will eventually wear out to the point where it needs an overhaul, and the "kinder" you are to your engine, the longer it will be before it wears out.

I'm not sure I'd characterize Bob Munro, one of the three founders of Kenmore Air Harbor and the pilot/mechanic who ran it for the next 54 years until his death in 2000 as "whacko" Kenmore Air, if you don't know, is one of the the world's most successful and long-lived seaplane operators/aircraft rebuilders. I suspect Bob knew that the pistons in an engine that ran for 10,000 hours before needing an overhaul went up and down a few more times than an engine that ran for 8,000 hours.

Anyway, I don't see how your statement "An engine that lasts a few thousand hours more than another one of the same [kind] because it was operated at a lower power has pistons that went up and down quite a few more times than its short-lived, higher power cousin" is any different than what Bob said--- "the easier you make life for the engine the more times the piston will go up and down." Unless I misinterpreted your statement.




-- Edited by Marin on Sunday 10th of October 2010 08:31:46 PM