Understanding Engine HP??? Caterpillar vs Ford Lehman?

The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
See posts with no answers
J

jefndeb

Guru
Joined
Jun 11, 2018
Messages
620
Location
US
Vessel Name
Indigo Star
Vessel Make
2006 Mainship 400
Hello,

We have been looking at used Trawlers at or around 40 Ft at or around $150k.

We have been leaning towards the Mainship 400 because is seems to fit our needs, both in budget and space....but I found a 1985 Kadey Krogen 42 that looks super nice, more room and its a Kadey!!!

But what I am confused about is the Mainship has a single Cat 380 HP diesel but the Kadey has a single Ford Lehman 135 HP...

What am i missing?? Why does the slightly smaller boat have so much more HP? Is it because is newer and engines are more advanced?

Thats over 3 times the HP....I guess there is something I am missing...

Comment welcome please...
 
Hull shape.

That Mainship, with a semi displacement hull, and with that engine can get 16 knots.

The Kadey is a full displacement boat, once you hit displacement hull speed you start to push water - so not efficient. Hence you only need a smaller engine.

The Kadey's displacement hull speed is around 8.7 knots, assuming water line length of 42, which is probably less at 38/39. (1.34 X the square root of LWL).
 
Last edited:
I suspect the kk42 might hit 8.7 at WOT. I suspect cruising speed to be closer to 7.8. However, at 7.8 I bet the boat is going better than 3kts per gallon.

I am sure Richard on dauntless can give us exact answers to this.
 
Others will respond I'm sure, but hull type is one reason. The Kadey has a "full displacement" hull, similar to a sailboat. Typically, speed of any hull (known as hull speed) is a function of its waterline length,. Google "hull speed formula". A full displacement hull is seaworthy and very efficient but it's speed is limited to hull speed or very close to it. Generally speaking, it doesn't have a lifting component in its design so it can't get up "on plane" to increase speed above hull speed no matter how much horsepower the engine has. The Mainship hull its sometimes called modified planing and sometimes semi-dispacement. In any case, it has a lifting component & will plane or at least get partially up to allow a speed increase above hull speed, but it takes a bunch of power (and fuel) to do it. The Krogen hull is very seaworthy and KK42's can and have crossed oceans. The Mainship is a capable boat, but is a bit more "tender" in open water. So which boat? Depends on where you plan to travel with her. Like I said, I'm sure others will chime in.
 
Only a handfull of FD trawlers here on TF.

Most all are SD as people are accustomed to the large engines of planing craft but more importantly speed. Visualize ... my boat (30’ 8 ton) in a boat show. Man says I like that boat. What engine she have? The salesman says 37hp 4 cyl. The man is astonished. NO... WAY I’m going to look at that one over there. It’s got about 100hp.
And the next guy comes along and asks “how fast is that boat”. The salesman says “six or 7 knots”. Guy says “hey I can almost walk that fast”. I’m going over and look at that other boat. Looks more like a speedboat.

Nothing’s really changed. FD (slow) boats aren’t any more in demand than SD. People still like speed and power. Just like the cars of the 60’s and 70’s. And interestingly most Trawler owners grew up in the 60’s or 70’s. And my Avalon has closer to 300hp than 200hp. It’s nuts. The Toyota Camry 4 cyl engine would have plenty of power for the Avalon but no ... it gets 277hp. Can still hear the kid say’in “betcha my dad’s Merc can go faster than your dads wimpy Pontiac”.

But in Trawlers there is the weekend component. Lots of space out there and so little time.
 
I have the slowest boat in our club, and that includes dinghies and, I suspect, most of the sailboats. :facepalm:
 
Yes, most of our boats are not full displacement trawlers but rather semi displacement which can use the extra horsepower to go faster. Full displacement boats like the KK 42 do not benefit from more horsepower. Add a lot more power to the KK and it will make a big wake and burn a bunch more fuel and go slightly faster. FD boats need X amount of HP and a bit more for wind and current. X HP isn’t as much as you might think for a FD boat. On the other hand a semi displacement boat can use quite a bit of power. My boat model was built with twin 120s up to twin 275s because it is a semi displacement hull. With the 120s it is operated similar to a FD hull. With the larger power it can be run up almost on plane, just uses a whole lot more fuel.
 
jefndeb said:
Hello,

We have been looking at used Trawlers at or around 40 Ft at or around $150k.

We have been leaning towards the Mainship 400 because is seems to fit our needs, both in budget and space....but I found a 1985 Kadey Krogen 42 that looks super nice, more room and its a Kadey!!!

But what I am confused about is the Mainship has a single Cat 380 HP diesel but the Kadey has a single Ford Lehman 135 HP...

What am i missing?? Why does the slightly smaller boat have so much more HP? Is it because is newer and engines are more advanced?

Thats over 3 times the HP....I guess there is something I am missing...

Comment welcome please...
Click to expand...

The Mainship has the 380hp so they can say it has a top speed of 16kts which sounds really great. The reality is that the fuel mileage at 16kts is so poor that nobody except the rich would run it at that speed for any length of time. We're talking .7mpg vs 2-3mpg. If one only runs a few miles to the sand bar and back, 16kts is great. For anybody doing long range cruising, the .7mpg is prohibitive.

The KK has a much more realistic HP that is very adequate for the type of use the boat was intended.

Keep in mind that most trawlers in the 4x' range need only about 60hp to run at 6-8mph which is the speed range that most are run at.

Ken
 
OK, so basically since a full displacement type hull cannot get on plane due to its design, an engine that has less HP is sufficient to push through water were as a Semi Displacement hull that can partially get up on plane needs this extra HP to get up on plain although its not very fuel efficient to do so..do I have this right?
 
The boat in our avatar is a 38' full displacement hull. We run between Toronto and Abacos at 7knots using 0.75gph with a 55hp diesel. We can force 8knots but fuel useage triples (at least) and it get noisy ..... Thats the difference in a nutshell.
 
jefndeb said:
OK, so basically since a full displacement type hull cannot get on plane due to its design, an engine that has less HP is sufficient to push through water were as a Semi Displacement hull that can partially get up on plane needs this extra HP to get up on plain although its not very fuel efficient to do so..do I have this right?
Click to expand...

However that semi displacement hull can also be run at hull speed with very low HP. Grand Banks trawler is an example of a semi displacement hull that can be equipped with a low HP engine designed to be run at 7-8 kts or twin high hp Cats To get it up on plane......using lots of HP and fuel.
 
Too much teak decking for this sailor... but then again, I'm getting lazy in my old age... :)
 
I am recaulking my teak sundeck this winter. Never again. A good friend had a full displacement Defever. We could not sit aboard it for more than a half hour due to the motion, my wife would start getting ill.
 
boatpoker said:
The boat in our avatar is a 38' full displacement hull. We run between Toronto and Abacos at 7knots using 0.75gph with a 55hp diesel. We can force 8knots but fuel useage triples (at least) and it get noisy ..... Thats the difference in a nutshell.
Click to expand...

Wifey B: And the boat currently in our avatar is 44' planing hull. We run between Key West and Daytona and sometimes the Bahamas at 35-37 knots averaging 0.66 nmpg with twin 800 hp diesels. We can force 42 knots. Not as noisy as you might think as 74-75 decibels at cruise.

In a nutshell it's all very different type boats for different uses. Now we have a boat we cruise slower and further in but nothing that is full displacement or truly close to a trawler. You have to figure out what your need and desires are and match the boat to them. :)
 
Comodave said:
I am recaulking my teak sundeck this winter. Never again. A good friend had a full displacement Defever. We could not sit aboard it for more than a half hour due to the motion, my wife would start getting ill.
Click to expand...
Geez, we've owned our DeFever 44 for five years, lived aboard for over two years, are presently 4,000 miles into a Great Loop cruise and have had no problem with the "excessive" motion you describe. In fact, we have found it to be quite stable. Yours is the first time I have ever heard a complaint of this type about a DeFever.
 
Generally, a full displacement boat will roll more than a hard chined semi-displacement boat when in a beam sea. Although the tendency to roll is more, it is a softer roll without the snap action that a hard chined boat gets in a side on swell.

Some like it, some don't.
 
"OK, so basically since a full displacement type hull cannot get on plane due to its design, an engine that has less HP is sufficient to push through water were as a Semi Displacement hull that can partially get up on plane needs this extra HP to get up on plain although its not very fuel efficient to do so..do I have this right? "

Close , the rounded hull Can be pushed up on its bow wave , it just takes MASSIVE HP or a skinny boat that makes a smaller bow wave.

During WWI good speed was obtained with triple engines , a massive fuel supply and a WL L/B ratio of better than 6-1.

Herrishoffs "Marco Polo" series of motor sailors were able to cruise at 10K as they were fine on the waterline.

For cheap travel the full displacement boat run at about the SQ RT of the WL (not hull speed) only takes about 3 HP per ton of displacement .

2240lbs per displacement ton. Hull speed can be 5HP per ton or more.

So a 44,800 boat will need only 20HP in the water , to cruise , a bit over a gallon an hour.

Larger engines are installed so alternators , bilge pumps and other goodies can be engine driven.

As non industrial engines are peak rated , not cont rated.

,A cruiser can be fitted with an engine rated with over "100" hp , although in most cases it uses 2 or 3GPH , or 30 -55HP long term.

IF the eng. mfg. has a table of rpm/hp ratings from M1 to M4 it is usually an industrial engine.

IF not the engine will be OK of only loaded to 1 hp for every e CI of displacement , or so.

Good hunting.
 
Last edited:
jefndeb said:
Is it just me or is this an unbelievably beautiful boat....good price as well!!

View Yacht - Kadey-Krogen Yachts, Inc. : Kadey-Krogen Yachts, Inc.
Click to expand...

It does sound very good.
I like the two head model and this boat also has a lot of extras that make it very nice. I think it's a good, fair price, as long a it is as described.

I would like to know what her previous name was, if anyone knows.

One thing I will add about semi planing or semi displacement hulls.
If i have 28 miles to go. With my full displacement hull, I know it's going to take 4 hours. Doesn't matter what the wx is going to do, hurricanes, tornadoes, Svr CAT, doesn't matter, it's 4 hours and we must be prepared.
But i needed that full efficiency, 4.15 nm/gal, to cross oceans.

If i wasn't crossing oceans and most aren't, a good case can be made that it's nice, sometimes convenient, certainly more comfortable to have the option to make that 28 mile trip in 2 hours or less.

It's one of the reasons SD boats are 98% of the market.
 
AusCan said:
Generally, a full displacement boat will roll more than a hard chined semi-displacement boat when in a beam sea. Although the tendency to roll is more, it is a softer roll without the snap action that a hard chined boat gets in a side on swell.

Some like it, some don't.
Click to expand...

And with my Kadey Krogen, the rolling doesn't take any power, though the rolling itself is a function of speed.

In other words, at a given rpm and power, the speed and therefore consumption is the same whether rolling or not (not stabilized).
And in the same beam seas, the faster I go, the more it rolls.
 
jefndeb said:
OK, so basically since a full displacement type hull cannot get on plane due to its design, an engine that has less HP is sufficient to push through water were as a Semi Displacement hull that can partially get up on plane needs this extra HP to get up on plain although its not very fuel efficient to do so..do I have this right?
Click to expand...

Yes, but at slower speeds The SD will use similar fuel as the FD hull. IMO the option of going fast when desired is nice to have. You get to decide.
 
The KK42 the OP is referring to is under contract.
 
SD hulls have a lot more drag than FD hulls. For most of not cruising oceans the difference is insignificant. However, that extra .5 nautical mile per gallon could add up to 500 more miles of range.
 
"I would like to know what her previous name was, if anyone knows. "

Richard... Krogen Cruisers is showing her previous names were:

Ben Addiction; Graves End, Summers Beginning II
 
jefndeb said:
Is it just me or is this an unbelievably beautiful boat....good price as well!!

View Yacht - Kadey-Krogen Yachts, Inc. : Kadey-Krogen Yachts, Inc.
Click to expand...

Definitely a very beautiful boat and appears to be well preserved. Whether it is well priced is up to you - it all gets very subjective. My only hesitation is with teak planked decks. A KK is not one of those generic Asian trawlers known for leaky/soft decks. But sooner or later they’ll all need more work regardless of the build quality. 33 years is a long time. But that’s just (nervous) me with limited funds. :ermm:

It’s beautiful and maybe perfect for you!
 
Wxx3 said:
And with my Kadey Krogen, the rolling doesn't take any power, though the rolling itself is a function of speed.

And in the same beam seas, the faster I go, the more it rolls.
Click to expand...

Interesting.
With my displacement boat the rolling is slightly reduced with more speed. This may be the bilge keels stabilising the roll.
 
You must log in or register to reply here.

Similar threads

Adopo
Anyone have Lehman SP355?
Replies
6
Views
1K
DavidM
DavidM
Caballero II
GB 36 rudder authority
2
Replies
31
Views
2K
Caballero II
Caballero II
bill209
Importing a boat from Canada - Ford Lehman question
Replies
19
Views
2K
WeekendR_Ken
W
Cargile
Gasser on the Great Loop?
2
Replies
43
Views
1K
slowgoesit
slowgoesit
bill209
Ford Lehman high rpm’s at idle
Replies
21
Views
3K
Comodave
Comodave

Latest posts

Back
Top Bottom