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Old 04-07-2015, 09:07 PM   #1
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80 hp vs 130 hp

I've been looking at 1980s vintage 40 foot trawlers with twin screws on yachtworld for a while, and most of them seem to have 130 hp and above engines. However, every once in a while, I will see one with twin 80 hp engines. I've seen them on a Defever 41 and a Krogan 42. Coming from a sailing background, I would think that two 80-something hp engines would be more than enough for a 40-something foot trawler. Why is it that 80-something hp just didn't seem to have been in demand back in the 80s? Would it be a mistake to buy one now?
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Old 04-07-2015, 09:47 PM   #2
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In floatplanes and boats, there's no such thing as too much power.

We would never buy a 40 foot boat with two 80 hp motors. Sure, they'll shove the thing along at the typical creep speed for this kind of boat. It it's a displacement boat like a Krogen, then there's a point at which having more power has no value as you're limited by the hull speed.

But most cruisers of the type most of us on this forum own have semi-planing hulls, which means if you have the power you can use it to go faster if you want to.

The boat we have in the PNW, a 1973 Grand Banks, is an eight knot boat because of the engines that are in it which total 240 hp (two 120s). But later versions of the same boat have 440 horsepower (two 220s) and they can be cruised at 10 or 12 knots or even more if one really wants to push it. Same hull as ours, but more power.

A lot of boaters want to get somewhere fairly quickly, cruise around for a week or three at a leisurely pace, and then beat feet home. This lets them get the maximum time in the area they want to cruise around in and spend the minimum time getting there and back. Very important to someone with a limited a mount of time to take a cruise.
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Old 04-07-2015, 10:06 PM   #3
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At "trawler" speeds, boats at 40-something-feet and less don't need more than a single 80-horsepower engine. Still, an express cruiser will need lots horsepower, usually but not necessarily multiple engines, and a suitable hull to get beyond hull-speed.
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Old 04-07-2015, 10:13 PM   #4
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80 hp vs 130 hp

Quote:
Originally Posted by Marin View Post
In floatplanes and boats, there's no such thing as too much power.

We would never buy a 40 foot boat with two 80 hp motors. Sure, they'll shove the thing along at the typical creep speed for this kind of boat. It it's a displacement boat like a Krogen, then there's a point at which having more power has no value as you're limited by the hull speed.

But most cruisers of the type most of us on this forum own have semi-planing hulls, which means if you have the power you can use it to go faster if you want to.

The boat we have in the PNW, a 1973 Grand Banks, is an eight knot boat because of the engines that are in it which total 240 hp (two 120s). But later versions of the same boat have 440 horsepower (two 220s) and they can be cruised at 10 or 12 knots or even more if one really wants to push it. Same hull as ours, but more power.

A lot of boaters want to get somewhere fairly quickly, cruise around for a week or three at a leisurely pace, and then beat feet home. This lets them get the maximum time in the area they want to cruise around in and spend the minimum time getting there and back. Very important to someone with a limited a mount of time to take a cruise.

Yah. You can't get your Krogen 42 on the plane with twin 80's you know. Or twin 871's for that matter. More power please!

Actually I think a Krogen 42 would push along just fine with an 80 hp Lehman.


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Old 04-07-2015, 10:20 PM   #5
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Quote:
Originally Posted by seattleboatguy View Post
I've been looking at 1980s vintage 40 foot trawlers with twin screws on yachtworld for a while, and most of them seem to have 130 hp and above engines. However, every once in a while, I will see one with twin 80 hp engines. I've seen them on a Defever 41 and a Krogan 42. Coming from a sailing background, I would think that two 80-something hp engines would be more than enough for a 40-something foot trawler. Why is it that 80-something hp just didn't seem to have been in demand back in the 80s? Would it be a mistake to buy one now?
The difference between the 80 and 130 hp is often an increase in cylinders from 4 to 6. Some claim the older 4 cylinder engines vibrate more. Going to the 130 will gain a little speed at WOT at the expense of fuel economy. A few more modern vessels such as the Great Harbours and Endeavour Powercats were powered by Yanmar engines in 80 hp range.

If the 80 hp engines are well maintained and you are content to cruise at displacement speed, it becomes a matter of preference and not right or wrong. I would be more than happy with a Great Harbour or an Endeavour.
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Old 04-07-2015, 11:49 PM   #6
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Going from 160 total HP to 260 will probably give you about 2 knots more top end for about 5-6 gallons per hour higher fuel consumption. The advantage of the higher power engines is that you will be able to cruise at lower rpms - i.e., quieter. The only other advantage I see to more power is that you might get better resale because people generally don't understand how little power a trawler needs at displacement speeds. For example, my 32' pure displacement cruiser only has a 40 hp diesel and I can cruise comfortably at 7 knots with about a 9 knot top end. Before I put that engine in the boat had 120 hp and could hit 12 knots.
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Old 04-08-2015, 12:01 AM   #7
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Yah. You can't get your Krogen 42 on the plane with twin 80's you know. Or twin 871's for that matter. More power please!

Actually I think a Krogen 42 would push along just fine with an 80 hp Lehman.
I'm sure it would. However, with a displacement cruiser one must be satisfied with creeping along being passed by glaciers and stuff. My wife and I don't have the patience for that (anymore).

"No such thing as too much power" applies to machines that can take advantage of the power. I'm not implying that one should put a ton of power in a boat that can't make use of it.
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Old 04-08-2015, 12:17 AM   #8
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Another thought about using the correct engine is the displacement to power ratio. When you ask an 80 hp engine to push a boat at say 6 kts that little engine might be putting out %80 of its available power. On the other hand a 250 hp engine might only be using %25 of its available power and the reliability and longevity factor will go way up.
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Old 04-08-2015, 12:25 AM   #9
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Originally Posted by Marin View Post
In floatplanes and boats, there's no such thing as too much power.

We would never buy a 40 foot boat with two 80 hp motors. Sure, they'll shove the thing along at the typical creep speed for this kind of boat. It it's a displacement boat like a Krogen, then there's a point at which having more power has no value as you're limited by the hull speed.

But most cruisers of the type most of us on this forum own have semi-planing hulls, which means if you have the power you can use it to go faster if you want to.

The boat we have in the PNW, a 1973 Grand Banks, is an eight knot boat because of the engines that are in it which total 240 hp (two 120s). But later versions of the same boat have 440 horsepower (two 220s) and they can be cruised at 10 or 12 knots or even more if one really wants to push it. Same hull as ours, but more power.

A lot of boaters want to get somewhere fairly quickly, cruise around for a week or three at a leisurely pace, and then beat feet home. This lets them get the maximum time in the area they want to cruise around in and spend the minimum time getting there and back. Very important to someone with a limited a mount of time to take a cruise.
My sentiments exactly! That's why I own a Tollycraft... among several other important pleasure boating features.
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Old 04-08-2015, 12:38 AM   #10
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I'm sure it would. However, with a displacement cruiser one must be satisfied with creeping along being passed by glaciers and stuff. My wife and I don't have the patience for that (anymore).

LOL. It was such a gentle dig! For me it's all about the space. And with the pilothouse, it's like driving around in your living room.


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Old 04-08-2015, 01:22 AM   #11
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A while back I saw an IG32 with twin Lehman 80s, I think they would have been perfectly adequate. Recently I saw one advertised with twin 200hp Volvos. Good grief!
If you find a good 40 with good 80hp twins, try for an early sea trial run. That should tell you more than posts, however well intended.
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Old 04-08-2015, 01:50 AM   #12
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For me it's all about the space. And with the pilothouse, it's like driving around in your living room.
Krogens are great in that regard. My wife and I feel they are excellent designs.
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Old 04-08-2015, 03:03 AM   #13
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LOL. ... For me it's all about the space. And with the pilothouse, it's like driving around in your living room.


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Old 04-08-2015, 06:49 AM   #14
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Another thought about using the correct engine is the displacement to power ratio. When you ask an 80 hp engine to push a boat at say 6 kts that little engine might be putting out %80 of its available power. On the other hand a 250 hp engine might only be using %25 of its available power and the reliability and longevity factor will go way up.
Let's not forget that diesel engines want to see some load. I'd be concerned if I was constantly running my diesel engine at 25% of its available power. I can't recall the exact percentage, but my cruise RPM equates to 70%-80% load (around where Volvo says it should be).

This has been discussed extensively on the forum.
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Old 04-08-2015, 07:47 AM   #15
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I'm sure it would. However, with a displacement cruiser one must be satisfied with creeping along being passed by glaciers and stuff. My wife and I don't have the patience for that (anymore).

"No such thing as too much power" applies to machines that can take advantage of the power. I'm not implying that one should put a ton of power in a boat that can't make use of it.
Marin, If hull speed bothers you so much, why don't you loosen up the purse strings, put a pair of 300+ HP in your boat, and make it plane. Until your boat gets on top, you're just another displacement vessel plowing in denial.

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Old 04-08-2015, 08:06 AM   #16
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Originally Posted by JDCAVE
For me it's all about the space. And with the pilothouse, it's like driving around in your living room.

Quote:
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Krogens are great in that regard. My wife and I feel they are excellent designs.
JD - With due respect

I agree with Marin and wife in statement above... however... I don't boat to feel as though I'm in my living room. Could inexpensively stay home for that. I do boat to be ever closer with the elements in regard to flying bridge piloting in open air and as much swimming as possible.

As in all human endeavors regarding fun and enjoyment - "different strokes for different folks!"

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Old 04-08-2015, 09:43 AM   #17
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Frankly, if you want to go considerably faster than hull speed, then you don't really want a trawler. For a displacement hull form, the power requirements increase almost exponentially at speeds above hull speed. Here is the power curve for my boat showing horsepower required at different speeds. The nominal hull speed (1.34 x square root of LWL) for my boat is 7.6 knots. At about 7 knots my boat needs around 20 hp, but at 10 knots the power requirement is more like 60 hp. If I extended the calculation to 12 knots the power requirement is around 120 hp.



Remember that going faster not only requires much more power, but also requires proportionately more fuel. A typical diesel will burn about 1 gallon per hour for each 18 horsepower it produces. So going from a speed that requires 72 horse power to a speed that requires 250 hp will increase your fuel burn from about 4 gallons per hour to about 14 gallons per hour. For a 40 foot trawler the speed increase will be from about 8 knots to maybe 12 knots. Take a Nordhavn 40 as an example. Those boats are heavy displacement 40 footers (50,000 lbs), yet they are powered by a 105 hp diesel. That boat needs only 27 hp to run at 6 knots on flat water, so the 105 hp engine will not push the boat much over 10 knots. Doubling the power might get you 12 knots. At 6 knots a Nordhavn 40 will burn about 1.5 gph and at wide open throttle no more than 6 gph.
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Old 04-08-2015, 10:11 AM   #18
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I am a little late to this discussion, but it seems that the OP's original question- Are twin 80 hp engine adequate for a 40+' trawler, depends entirely on the boat and how you use it.

Looking at Bebe's book with Lieshman edits, James Krogen provided speed vs hp data for the Krogen 42. That boat is very easily driven as it is a pure displacement hull. According to Krogen's data it takes a bit more than 50 hp to push it to 8 kts. So 160 hp would be totally adequate. Even a single Lehman 120 would work fine.

The Defever 41 that the OP mentioned may be a different story. It is a semi-displacement hull and even though it is about the same size and weight as the Krogen it might take 50% more hp to push it to 8 kts due to its hull shape. Even still if all you wanted to do is cruise at 8 kts 75 hp out of 160 would be totally adequate as well. But if you wanted to push it faster, well you need more hp and a pair of Lehman 120s would be better.

Then to the other question implied by the OP: how will a pair of 80 hp engines perform? Well, if they are 4 cylinder Lehmans they will perform fine, but will probably be a bit rough at low rpms. But a newer John Deere 4 cylinder 85 hp engine has a balance shaft which should make it lots smoother.

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Old 04-08-2015, 11:12 AM   #19
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"No such thing as too much power".

Hawgwash. There's tooooo much power almost, everywhere.

Every vessel has a design speed, displacement and power requirement. Sometimes a designer may spec 80hp for a boat and get told to up that from marketing people. 80hp would definitely be perfect for the 42 Krogen as evidenced by the Performance curves. And the manufacturers recomend 50 - 75% load so there should be no argument. Just good engineering.

But the best of engineering dosn't sell boats. David's point is spot on and others that mentioned resale. We live in a world of automotive mentality whereas my VW Jetta has 170hp. People can't relate to a boat weighing many tons being pushed along well with less power than a small car .. but of course it's a fact they do just fine.

Four hp per ton of vessel weight is all that's required for a FD craft. SD varies but on the average hull on this forum 6 to 7hp per ton does the job. Any more power and it's just the greed for speed or imaginary notions like outrunning a storm. Marin knows this ... he's just stiring the pot here. Some trawler boats that have a hull more like a planing hull can have more varied power installed to meet the requirements of buyers. But most trawlers should have a different hull shape if the power installed is raised or lowered. The marketing people aren't engineers and frequently don't listen to engineers either. Add the automotive mentality and that = most trawlers being overpowered. The goal for boat builders is to sell boats and make money. And I don't mean that too critically either. If I was building GB 32 boats the Lehman 80hp engine would by all engineering standards be perfect but I'd put the 120hp engine in the boats. Building one for myself it would get about 80hp .. or twin 40hp.

But power excites and excitement drives the market.
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Old 04-08-2015, 12:02 PM   #20
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Frankly, if you want to go considerably faster than hull speed, then you don't really want a trawler...
I have really enjoyed this discussion. Many thanks to all who contributed.
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