Total and Reserve Power

Mako

What brand, model and HP rating?

In a passagemaker magazine (June 2001) there is an article about a 60' 80 ton wood boat the Nathaniel Bowditch that was powered by an eight cylinder Gardner of 152hp. That equates to less than 2hp per ton. That's the lowest power per ton I've heard of. No speeds were mentioned and long ton or other weight spec was mentioned. If it dosn't specify long tons I assume 2000lbs per ton.

My own personal yardstick limits an acceptable power to weight ratio of 3hp per ton. I've compared lots of boats that have stood the test of time and three hp for every ton seems more of less the practical lower limit.

Early on Bob Coffer wrote;
"You can always throttle down but if you are under powered at some point you have no options.

Who knows where that line is? I know there have been times that I have wished for more."

"no options"?
Not so at all. I used to think that. But it's really not true. If you guess 10 or 20hp too little power you just run a little slower. But it's not proportional. If you gain 30hp and gain .25 knots on the same boat if you were to loose 30hp you may only loose .10 knots. Those numbers are just for example.
There's no line. It's all a big grey area. We don't fall off the edge of the earth if we can't reach hull speed. If you guess too low you loose a bit of speed but very little as the power requirement is on a very nonlinear curve. If I had chosen 30hp (instead of 37) for Willy I'd probably be going the same speed as I go now w 5hp per ton (37hp). And if I worked the smaller engine the same as the larger I'd probably be going 6 knots instead of 6.15.
So you don't "run out of options" .. you just go a tad bit slower.
And Bob if you wish for more and get more almost immediately you'll be wishing for more again. The answer is not to wish for more.

manyboats said:

I've compared lots of boats that have stood the test of time and three hp for every ton seems more of less the practical lower limit.

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Perhaps some romsdahl or malahide owners will chime in, but if I recall correctly they are generally powered about 3.2 to 3.5 hp per ton.

sunchaser said:

Mako

What brand, model and HP rating?

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AGCO SISU 49CTIM 180 hp

Good engines and well regarded company. They have pretty well blanketed the farm implement business with this same base engine.

I can see why you are reluctant to go bigger in CID/HP as the next size up is much larger, more money and heavier. In this HP range properly marinized engines other than your selection are few - JD, Lugger and Perkins Sabre/Cat 3056 ( I have two) amongst those few. Are you using a keel cooled setup?

Prop selection seems the remaining question, are you there yet? Good job Mako and interesting post.

If expecting to cruise at 140hp on a 180hp 2300rpm engine, that puts it about 2080rpm on the 2.5 prop curve. Engine should be happy there, but probably not the best for bsfc nor the best for noise/vibration. That engine looks to be a 4cyl without balance shafts, and that has a second order vertical vibration that may be obnoxious. That's why it is rare to see 4cyl in boats, where you see lots of six cyl. The six has near perfect balance.

A good rule of thumb is to size engine so under cruise conditions you are around the same rpm as full power torque peak, but obviously not at full power. You are way above that rpm.

Sizing engines for planing boats is different, you need the power but not the weight, so in those cases you expect the engine to run hard. Not the same for spec'ing for a trawler.

manyboats said:

Why do you say "maintain speed"? Why not just slow down?

Also there is no need to reach hull speed on a FD boat. I'm not even sure Willy can attain her HS of 7 knots. I wish the expression "hull speed" had never been coined. It's very misleading in many ways. A boat very similar to Willy at 5hp per ton (2000lbs) w less power probably would not be capable of HS. There's fast boats, slow boats and slower boats. Hull speed is just a mathimatical expression. And there's no need to go at HS ever. Most FD skippers wisely cruise a knot below HS and working the engines hard the FD boat is still closser to one knot below HS than actual HS. Providing the boat is not overpowered. You'd be better off forgetting about hull speed.

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I never mentioned hull speed and agree I wish it had never been coined.

I had a full displacement boat probably similar to yours in many ways and trying to come north along the CA coast I assure you I needed more power to maintain speed. Each wave stopped the boat and it would then reaccelerate just in time for the next wave. More power would have overcome the waves.

I am enjoying this discussion because I know nothing about it. Most of the discussion has gone completely over my head.

When you discuss hp/ton, what figures are you using? I assume max rated hp, but is ton the displacement, dry weight...?

Any idea what some hp/ton ratios are with some well known FD production vessels such as Nordhaven, KK, or Selenes?

Mako

As a reminder to us ditherers, what is the WLL and weight of your vessel?

To Ski's point about 4 cylinder harmonics and vibration, any thoughts? Four cylinder JDs, Luggers and Perkins Sabres are no problem according to owners in this regard, but on your planned engine --?

when waves are high, I have to lower power to reduce violent boat movement.

Mark .....
Same here. And of course we slow down. Lots of people don't like slowing down. Slowing down is part of life and it should be done ...... when it should be done. What did you say? ..... slicers and bashers?j

Since my boat isn't a tall, floating condominium, wind seems to have little effect on power needs.

Using additional power in some sea situations keeps the speed up and minimizes the duration greatly without seriously changing the intensity of "bashing" ... which sounds like good seamanship to me.


I have done it many a time...as well as slowed down when it was the only solution to self preservation.


No one solution fits all....

Here is a list of hp/1000lbs for several Nordhavn's. Note: This list was copied and pasted from a Nordhavn owners blog where he talks about how he decided on how much horsepower was appropriate for his then yet to be built boat, a Nordhavn 52.

· N40: 3.30 (50,000 lb @ 165 HP)

· N43: 2.75 (60,000 lb @ 165 HP)

· N43: 1.75 (60,000 lb @ 105 HP original engine)

· N46: 1.75 (60,000 lb FD @ 105 HP)

· N47: 1.94 (85,000 lb FD @ 165 HP)

· N50: 3.75 (80,000 lb FD @ 300 HP)

· N55: 2.66 (124,500 lb FD @ 330 HP)

· N57: 2.66 (122,000 lb FD @ 325 HP)

· N62: 2.19 (155,000 lb FD @ 340 HP)

Below is a link to the blog written by James Hamilton who owns the Nordhavn 52 Dirona. In his blog he discusses some points that some here may find interesting, especially for anyone who is contemplating how much power is needed for their future full displacement boat.

Experience with John Deere 6068AFM75 in Nordhavn 52 | MV Dirona

Here are a few hp per ton numbers.
My little boat is 5.

N40 6.6
N46 6.6
N57 5.3
N47 3.8

I see the N62 is about 4.5 hp per ton.
I think Mako you alluded to the notion that bigger boats have less power per ton. This becomes evident in the single brand comparison.

Thanks for the info and that link. I was curious because reading you guys talk about 4hp/ton reinforced in my mind the idea that many of the modern FD trawlers are way over powered. Who really wants to drive a trawler at 15 knots?

Even my 40' sailboat has 5hp/ton. Maybe that explains why I use such a small amount of its available power?

Dave I think most sailboats have much less power than properly powered FD trawlers. Part of that is because sailboats have very low prismatic coefficients (PC) and require less power. Since a sailboat must be powered by only wind power most to all of the time their hulls ore optimized for low resistance. Trawlers not so much.
Also there are motorsailers intended to be powered 90% of the time and those that wouldn't be caught dead running their engines over 5% of the time. So the NA designs the boat to cater to a variety of intentions and needs.
Your boat seems a bit overpowered for a sailboat. Perhaps that was a sign you were destined to become a trawlerman in time. May out world become yours.

Thanks for the link Diesel Duck.
Very interesting indeed. I love the open mindedness that he approached the question. He was just as open to less power as he was more. His N57 is the same power loading as my small Willard and my Willard (even though she's been repowered) has the same power loading as she did when new. Willard got this right on the 30' boats built before 1990.

Power was his primary reason for choosing the Deer and my primary reason was also power. I wanted two other engines. One had a high mounted starter and a bit too much power (47) and the other had unquestionably too much power .. 54hp. So I went w the 37hp Mitsu.

My KK54 has 225HP for 68,000lb dry weight. That's 6.6 HP/short ton. In practice the boat probably weighs more like 80,000lb loaded so that would be 5.6 HP/short ton.

Richard

There is nothing evil or sinister about having too much installed HP. Why all the angst over the subject when 99% of us already own the boat and are locked into the HP we have? IMHO it is the hand on the throttle that determines actual fuel consumption, not installed (and seldom used) HP.

Mako is a rare exception, he is still trying to determine what makes sense to him. To conjure up some what ifs we can get out the slide rules and play Walter Mitty and fantasize over something we seldom if ever are able to do on our own craft.

Or just fit into the notch of the Nordhavn vessel information provided by Diesel Duck. The real fun part of this is what engine will work best, rattle least and be cost effective in the + or - 200HP range.

Good morning! I'm about 8-11 time zones ahead of most of you and when I wake up there's a lot to catch up on. This has turned out to be the most useful thread BTW. Luckily I have time before we start cutting steel to make a final decision (thank God). Here are some of my thoughts and responses:

UNITS - We all should standardize on the same units when talking "tons." Generally aren't naval architects using long tons (2240 lbs)?

SPECS - My boat was designed with a displacement of 56.5 cubic meters of seawater at DWL. 56.5 long tons. It's LWL is 47 ft. Tranny is 3.46:1 ratio and prop is calculated at 37"x23" in a 3 blade fixed. We don't need the Kort nozzle in the original design.

However, I have changed from a transom stern to a beautiful horseshoe and it is now radius chine (24 inch radius). So the numbers will change slightly, but not dramatically. Yes it is keel cooled and I instructed them to remove the beautiful Duramax keel cooler from the design and replace with welded split pipe. The engine is too small to require high performance cooling (my shipyard specializes in tugs, which have different needs).

VIBRATION - I never noticed any particular problems with the SISU engines, and logically if there were big issues with vibration in the 4 cylinder version then the manufacturer would have worked it out or the engine would have been discontinued. Perhaps Sunchaser can comment.

RESERVE POWER NEEDED - My original post raised the question of what power would you guys install if you had an opportunity to repower, knowing that budget IS a concern? This is purely subjective of course based on individual needs.

PERFORMANCE - I've rerun the program and with parasitic losses the Vmax works out to 8.0 knots at DWL. So when I'm cruising at 7.5 kt I will be at 80% or more of power output, which for this commercial marine engine is acceptable (M1 rating).

PROPELLOR - If my budget allows, I can consider either a larger engine (hull can absorb up to 280 hp) or a CPP which has advantages and disadvantages as well.

CLOSURE - This is what brought up this discussion... there will be no more boats after this one for me and this custom design should reflect my personal preferences and experience from a lifetime of boating. I don't care about trends. Resale value is not a concern (although it will be for my kids when I'm floating in Valhalla). Reflecting on the past, I have always set my throttles and they have rarely wavered - except down, not up. Surfing down 25ft seas. Bashing into 12ft breakers. Quiet rivers. In a hurry or relaxed. Doubling fuel consumption for one extra knot isn't attractive. So the "reserve power" thing was never a big issue. Certainly there are a lot of sailors out there, on this forum, with a helluva lot more experience than I have and I really appreciate all the feedback and arguments. Anyway, no final decision yet as I'm trying to be open minded.

Thanks everyone.

Huh, let's see. Our Mainship is 26,000 lbs, two 454's, that's what, like 700 hp, so that's 54 hp per ton. Wow, such huge variations in hull designs and power profiles across boats.

Observing the rated peak HP of a vessel has little to do with the required cruise HP.

For many under 3HP per ton seems to be a sweet spot in terms of actual operation speeds and modest fuel use.

Few boats are engineered/built to operate with best efficiency , so if you figure you get perhaps 15HP per gallon ,real world, it is amazing what 30-50 HP will do with a 50,000 lb vessel!

Mako- regarding the vibration, on most commercial and industrial installs the "2x buzz" aka second order vibe of a 4cyl is no issue as NVH won't typically bother you on a tractor or generator. Also it intensifies with rpm so runnning 2080rpm it will be much more evident than tractor or gennie speeds of 1500-1800.

That's why the Deere 4045 and most larger automotive 4cyl have twin counter rotating balance shafts in the oil sump. The shafts spin 2x crank speed and cancel the vibes effectively. It does not appear the Sisu has these, but it may. Check on that.

Ski and Mako,

In the old days, Deutz diesels had balancing shafts driven off the engine, internal to the block. For some reason, they didn't put them on 'Industrial' engines saying that if it is mounted to a concrete pad a little extra vibration is no big deal. I disagree.

A SISU engine is an Agco engine, and Agco is a conglomerate that includes Deutz.

So, it may or may not have the counter balance shaft installed.

Also, most of my Deutz work was over 40 years ago, so things may have changed

Deutz engines had the best power and fuel consumption for many years until they ran into some miss-management problems. One interesting side note is that John Deere's factory is not far from Deutz and whenever Deutz had layoffs, JD would hire the engineers. Deutz complained to the courts but was laughed at. If you're not paying your engineers, they are free to go wherever they want....

So, as a result, John Deere's overall performance and efficiency has seen over 2x improvement in 30 years.

Also, the Deutz engine powered the Tiger tank used by Germany to fight world war II, using far less fuel than the GM designed American tanks. Also, since it was air cooled, no one could shoot out the radiators.

History class is adjourned.

Stu

As far as choosing the installed power FD boats are unique in that they have a very narrow range of power options. Installing more or less is almost stupid. It's not that way w any other hull type.

With a SD hull installing more power gives the option of going faster and is thus justfied. And that's the case w most TF boats. They are in a position to gain from more than 5 or 6hp per ton ..... but the FD hull or boat .. is not. So it's stupid to install more power than the boat can use. And getting close to hull speed at an engine load of 50 to 75% output is all the power that a boat FD boat can use.

Tom (sunchaser) I know where you want to go w this. A large number of skippers here want an overpowered boat so they can run it at low rpm. Run the engine at 1400rpm and 25% load. And many on top of that overprop to run at even lower rpm. With a FD boat that is just nonsense .. and it's not the smart thing to do most all the time w other boats as well but not real FD boats.

So Mako is doing the dance of ballancing all the variables and trying hard to hit the bulls eye. I applaud him as I know what he's going through. I was tempted to overpower Willy .. I'm proud to say I resisted and got it right. Mako will too ... basically he's already done it .. got it right.

As the link that DDR provided, when building Dirona, the Hamilton's went with a 265 HP engine. However, they have since had pretty major alternator upgrade.

"The final component upgrade to complete the system is replacing the 85A start battery charger with a 190A @ 24V alternator and installing heavier cabling for this larger alternator. The house battery bank already has a 190A @ 24V alternator so, in this new configuration, we have two 190A @ 24V alternators on the main engine. With the two alternators in aggregate, we have 9kw of power generation on the main engine. "

How much HP would these alternators require at maximum load?

Jim
Sent from my iPad using Trawler Forum

Guys, many of you are posting about how it is pointless to install more hp than needed. That is not the issue at hand.

Mako figures he needs 140hp going to the prop to cruise. The question is: What is the best engine to produce this 140hp? So are you suggesting installing 140hp and running it at 100%? Sure a continuous rated engine is capable of this, but is this the best choice? Even rated at C does not mean running at 100% is desirable, it just means it can handle it.

I have set up many propulsion systems which involved balancing weight, cost, efficiency, size, noise, vibes, etc, etc. For a trawler it often makes more sense to go with a larger displacement, heavier, lower rpm engine. Using fuel/hp/rpm data or better yet BSFC map, you try to pick an engine that is efficient and modestly load AT the point it is intended to operate.

Almost never is this up at high rpm. Usually best around peak torque rpm and 75% load, which turns out to be about half the engines rated hp. This puts the engine in overload if you power above that, but that is another topic beat to death!!

Mako has spec'd a 180hp to provide 140hp. Without going into all the numbers, it sounds to me that it is not the optimum engine. A larger engine, say the six cyl version of the same running at lower rpm may be better. This takes digging into the fuel charts which the mfr won't release.

They DO have the charts, so Mako you could ask them the following: With 140hp needed, what is the gph of the 4 and what is the gph of the 6 with each operating at its most efficient spot? In a couple minutes they can tell you that without releasing their precious charts.

I have been on so many boats and have been able to compare four cyl running hard to sixes running easy and the comparision is black and white. The slow six is MUCH more pleasant.

Also helps in the vibe department. Both at idle and at power.

Just trying help him make the right pick.

manyboats said:

Tom (sunchaser) I know where you want to go w this. A large number of skippers here want an overpowered boat so they can run it at low rpm.

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Eric, my point is quite simple. With but rare exception we all own a boat that has a given engine. No matter what the perfect theory is, few of us are going to yank out a perfectly good engine and install a smaller one to save a few dollars in fuel per year.

OC Diver is that rare exception. Kevin Saunders another, but less for saving fuel bucks and more for gaining entry to the 21st century. I'm sure there are a few others. Would those guys please raise their hands?.

Buying a new anchor to be in the current mainstream is simple. Repowering with a JD four banger that costs $25K before installation is something else again.

Mako is doing a new build and wants some advice. He is another exception. The question for him is what engine and what HP. Several salient points have been raised with JD talking about the 15 or so HP James Hamilton has installed for DC generation just another fillip.


Ski, I've queried AGCO about 4.9 vibration abatement. Be interesting to see what they say

Ski - I've sent a request to technical support to find out if the engine is fitted with twin counter rotating balance shafts or something similar.

Vibration aside, wouldn't fitting a CPP be the best solution as it would allow almost 100% load to be set at the 140 hp rating (1500 rpm, max torque, max efficiency) and also allow this at any other setting as well?

BTW - there isn't much difference in price between fitting a CPP and fitting a larger 6 cylinder engine.

Stubones99 - I checked with Deutz 6 months ago and the engines were only Tier 2 rated, not T3, so that eliminated them.

Where you intend to travel and the level of support and parts availability in those regions is an important consideration.


IMO boat makers choose a favored manufacturer to work with then pick the engine from within that makers list.


Rather than looking at HP per ton it might be interesting to look at engine displacement per ton. Engines can easily be hopped up for more HP.