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Old 12-03-2013, 08:26 PM   #1
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Over-powered trawler style boats

I hope I'm not breaking any rules by starting this thread with the comments on another, but Reubin Trane comments in the thread provoked me to bring this here. How many of our trawler style of boats are over powered, and why?

Originally posted by Reubin Trane

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Originally Posted by rjtrane View Post
We built the original Great Harbour 37s with a pair of Yanmar 39 HP diesels. During initial sea trials, we recorded top speeds of 8 knots plus.

The move to 54 HP motors was primarily a marketing move - to most shoppers, the 39s seemed too small. Of course, they weren't too small - just perceived as too small.

The larger motors do have the benefit of extra power for fighting headwinds and better single engine performance. Disadvantage, as perceived by some, was the larger motors had turbos while the smaller ones did not (IMO, turbos are a good thing if they are engaged/providing boost at cruising RPMs).

In other words, I agree with those who say that very modest HP motors are all that is required for cruising a boat efficiently - around 1 knot below theoretical hull speed (6-7 knots or so). It makes sense to choose a size that will get you to hull speed; any more becomes reserve power for against the wind and/or single engine performance.
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Old 12-03-2013, 08:45 PM   #2
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Very good question! Also I like the new avatar pic.
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Old 12-03-2013, 09:01 PM   #3
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With 300 turbo charged horses, I consider our 35' Mainship "extra", not "over" powered. Normal 8knot cruise we are probably only using a third of her power, while getting almost 3mpg. However, when called on, she can punch through the 15mph current of the Niagara River heading into Lake Erie. Nice to have the extra power when you need it.
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Old 12-03-2013, 09:04 PM   #4
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The original 10 out of the first 11 Krogen Manatees were fitted with 50 HP Perkins diesels, according to the Manatee database. There are still some around that haven't been re-powered. I spoke to a Broker some years ago that was offering one of the original Perkins powered Manatees. On a sea-trial in calm, Gulf Coast ICW water, he was able to obtain 7.4 knots in slack tide, turning a 22 X 13 wheel. After the first run of Perkins, the venerable Volvo 90 became the power of choice and was only later enhanced by 100 and 110 HP versions of the same engine respectively.

A popular boat publication showed a max of 7.5 knots from the 90 HP Manatee in shallow Biscayne Bay, near Miami turning the same 22 X 13 wheel. Jim Krogen invited them to re-test his own boat in deeper water where he claimed 8.5 knots was a more realistic top speed, but they refused and stuck with their own test results. Among Manatee owners with the Volvo 90, it is well considered that the majority of Manatees can reach this 8.5 mark or more. Some private experiments with larger, steeper pitched, or even 4 blade (vs. 3 blade) props produces complaints of increased suet collection on transoms and inabilities to reach max recommended RPM's, according to the old Krogen website.

Since the late 90's, some boats (including mine) have been re-fitted with mills producing up to 160 HP. but featuring identical peak RPM's and similar power curves. My own 140 Yanmar (turning the same 22 X 13 prop) will push my boat to over 9 knots while digging a huge hole. Other Manatee owners who have tested my boat say that they can feel the extra torque and acceleration, but I can't. It appears that everything that needs to be done on a Manatee can happen with 75 HP, and anything more is a waste.

With few exceptions (Kabota for one), manufacturers keep getting more HP out of the same displacement engines, and usually drop the lower HP series since they are no less expensive to build. Most recently, a flood ruined one of the old 90 HP Volvos and the Insurance company bought him a brand new 160 Volvo for a close bolt-in. Duh!? It seems that the more-gently turbocharged diesels are all but gone.

Photos below include the 50 Perkins, 90 Volvo, my 140 Yanmar, and my own boat's stern wave on the way to 9 knots.
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Old 12-03-2013, 10:23 PM   #5
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Quote:
Originally Posted by ronlord View Post
With 300 turbo charged horses, I consider our 35' Mainship "extra", not "over" powered. Normal 8knot cruise we are probably only using a third of her power, while getting almost 3mpg. However, when called on, she can punch through the 15mph current of the Niagara River heading into Lake Erie. Nice to have the extra power when you need it.
I feel the same way with the 660 horsepower in our Bayliner 4788

I can cruise slow and get great fuel economy.

When I want to go faster, to outrun bad weather, or to meet a schedule for example, 14 knots is only a push of the throttles away.

Overpowered, nope, just right.
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Old 12-03-2013, 10:31 PM   #6
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Uh Oh. Should I have said "Over Powered Full Displacement Boats"?
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Old 12-03-2013, 10:31 PM   #7
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There wouldn't be very many full displacement boats that aren't overpowered. You're right. Extra power sells boats. We are all big strong men that want big strong engines. grunt grunt.

Originally I was worried about being underpowered with my 36hp. Theoretically I'm about 50% overpowered. I rationalize it by saying I like the reserve hp to overcome wind & current. I probably only need 25% reserve to overcome wind and current, but in reality that is all I have available, as the raw water cooled block requires flushing and she starts to get a bit hot with the pedal to the metal. So the other 25% just allows me to delay some required maintenance.
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Old 12-03-2013, 11:02 PM   #8
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With 240hp combined our 60,000lb nearly full displacement boat is far over powered. Our hull speed is achieved at about 1500 rpm at which these engines are producing a fraction of their 2500rpm 120hp rating.
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Old 12-03-2013, 11:12 PM   #9
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Without considering the boat owners needs and the way he goes forth only full disp boats can be overpowered. They can only use so much .... 25hp in my case w a 30' Willard. Six hp per ton and more is overpowered for any FD boat. Two hp is minimum and about 4hp is Ideal .. maybe 4.5.

SD boats are all different re the amount of power they require and of course the needs of the owner. Marin w his 250hp GB 36 was close to spot on as he ran his engines at about 50% load and 8 (or so) knots. So for him the boat wasn't overpowered. I think the majority of older GB 36 boats cruise at 7 knots and for all of them the same boat is overpowered.

Most FD trawlers have a similar hull and disp (per volume) so have similar power requirements. Some like TAD's Yellow Cedar are designed for efficiency and require less. Some are beamy, chunky and otherwise not very efficient and those could require 5 or 6 hp per ton while very slippery boats like a narrow double ender would only need 2 to 3. But most FD trawlers need about 4 hp per ton.

The early Albin 25s had a 22hp two cylinder engine and was plenty but as hustler pointed out marketing often demands more power to sell the boats. So that's the reason most trawlers are overpowered. And unless you decommission some cylinders in the engine/s or take out one engine of a twin repowering is about the only answer. And the financial hit from loosing an engine is fairly high. One could always make a single out of a twin only to have the other engine die a year later. Finding used engines could be the low ball answer but a good replacement Lehman engine is frequently more expensive than I think it should be. I see occasional fish boat pull-outs on the cheap on Craig's List. Good engines like an Isuzu come to mind.
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Old 12-03-2013, 11:20 PM   #10
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What is wrong with extra power? I repowered my 44000 lb boat from 290 hp to 400 hp when I had the chance and haven't regretted a bit of it. I can go slowly and get way better economy than before the change, and I can go a little faster if I need to. With my Semi Displacement hull I can't get to a plane with only 400 hp total ( I think I would need at least 800 to plane) so any extra throttle after 8.5 knots is just digging a bigger hole. If I encounter conditions that require a little extra push, I have it and will use it. The rest of the time, I can enjoy slow, and economical cruising.
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Old 12-04-2013, 12:25 AM   #11
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I can think of lots of situations when that "over-power" and a little extra speed came in handy, In tidal currents at Dodd Narrows, Deception pass, crossing Straits of Georgia and Juan De Fuca in rough weather to name a few. There are times when fuel consumption and economy are the least of my concern.

It's all a matter of perception . . . With large engines, you always have the option of going slower, but with an undersized power plant you can't ever go any faster.
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Old 12-04-2013, 12:36 AM   #12
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Extra horsepower does not help a full displacement boat in tidal currents. If your maximum speed is 7 knots at full revs in still water, when you run against a 6 knot current, you will only be able to do 1 knot regardless of your extra horsepower.

The extra reserve in hp does come in handy pushing against the wind, as this is an additional force that needs the extra power to overcome it.
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Old 12-04-2013, 12:43 AM   #13
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There is a clear distinction between a displacement hull and a "semi-displacement" hull. A pure displacement hull just digs a bigger hole and pulls up a bigger wake with very little additional speed after it gets to a certain point. Any one that talks about going 9 or 10 knots cruise on a 36-40 foot waterline is clearly in the semi-displacement mode and burning way more fuel than I can afford. Not that 15 knots would not be handy at times......
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Old 12-04-2013, 12:51 AM   #14
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Quote:
Originally Posted by Edelweiss View Post
I can think of lots of situations when that "over-power" and a little extra speed came in handy, In tidal currents at Dodd Narrows, Deception pass, crossing Straits of Georgia and Juan De Fuca in rough weather to name a few. There are times when fuel consumption and economy are the least of my concern.

It's all a matter of perception . . . With large engines, you always have the option of going slower, but with an undersized power plant you can't ever go any faster.
Unless you turn around
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Old 12-04-2013, 05:56 AM   #15
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she can punch through the 15mph current of the Niagara River heading into Lake Erie. Nice to have the extra power when you need it.

The world dosnt work that way , as noted above .

Many times either the add dept picks the power level or the purchasing folks.

Wonder why there are so many Volvo powered boats?

The engines are frequently priced to be the lowest cost to OEM , who hardly care about maint costs after the boat is sold.

Most all 40-45 ft displacement boats that require smaller engines find the locker almost bare of 75 to 100HP heavy duty engines.
The 75 HP JD Jap marinization is too pricy for most entry level boats.

So they will go for auto rated taxi or farm equipment lighter duty engines that have high peak HP numbers but are useless at those ratings.

Underloading can be a problem but a 120-135 taxi/lorry rated diesel does just fine at 40 (2.5 GPH ) trawler crawling.

Best concept is to find the engines displacement and figure most can make 1 HP for each 3 Cubic inches and survive that loading long term..
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Old 12-04-2013, 09:36 AM   #16
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FF I totally agree, the more "iron" HP/CID the longer an engine will last (generally). Engines with high HP ratings from small displacement are high strung, running at high intake psi requiring large after-coolers and less tolerant of any abuse or lack of maintenance. Look at any yard doing re-powers and you will find the most replaced low hour diesel is the high HP small (lightweight) powered boats.

Yanmar while a good engine is not a high hour (5000+) engine and requires close attention. When the time comes to pull most are not rebuilt.

I was at a yard 5 months ago and looked in on an engine replacement where both Yanmar 370's were being replaced because of catastrophic failure of one and nearly to the other due to hard use (this boat would run 30's and did quite often). The engines had less then 600 hours on each.

They sure were lightweight for the hp, but aluminum, heat and salt water don't play well together, I was told the cause was after-cooler clogging and corrosion with subsequent overheating and warping with salt water ingestion.

Going fast costs a bunch of cash.
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Old 12-04-2013, 10:17 AM   #17
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I have a 49' 60,000 lbs. Grand Banks with twin Lehman 454CID 355 HP engines. I would be much happier with twin Cummins 210 HP. I am way over powered. Hatteras built their 58' LRC with 4-71 and 6-71 DD engines. For years the 4-71s were looked down on. Now with Fuel at $ 4.00 a gallon the hull value of the 4-71 powered vessel has come back up. 8.5 knots cruise with the ability to do 10 is perfect for my needs.
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Old 12-04-2013, 10:39 AM   #18
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The Kady Krogen 42 originally came with the Ford Lehman 120 then in ~1985 changed to the SP135. Later they came with either Perkins, John Deere and a few others but all 130 hp plus.

Fully loaded (44,000lbs) we need a little over 87 hp to reach a hull speed of 8.4 knots. To cruise at 7 knots we are only using ~51 hp. This assumes clean bottom, no wind, no waves, etc. We have 2 alternators and paravanes so the numbers would be a little higher but we are still not using the hp we have. The only time we have come close to using it is when we have towed other vessels and once when we were soft grounded and we able to power off. If we were to repower, I would probably go with ~100-110 hp.
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Old 12-04-2013, 12:20 PM   #19
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Well, if you are a purist and only accept the definition of a trawler as a round bottom, displacement hull cruiser, then that gives you one answer to the question. But even with that restricted definition of what is a trawler, those boats that meet that definition: Krogens, Willards, Nordhavns, some Selenes are not overpowered.

Specifically the Nordy and Krogen have engines that will easily drive the boat to hull speed and a bit more for wind, waves, etc. They efficiently cruise at about 1/3 of full power and at that power loading the engine will last forever.

But if you open up your definition to include most of the boats owned by members of this forum and those include mostly semi-displacement hulls, then these boats aren't overpowered for their mission either.

When we lived on the west coast we had a 2006 Mainship 34T fly bridge trawler. It looked like a trawler and at low power- about 40 hp, it operated like a trawler at displacement speeds. But that was only about 1/10 of its available hp of 370.

But I could if I wanted to, open it up to 200-250 hp and cruise at 12-13 kts. It wasn't very efficient at that speed, but it did what I wanted it to do.

Was it a trawler and was it overpowered? Only you can decide.

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Old 12-04-2013, 12:43 PM   #20
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Florida Bay Coasters- Key Largo & Florida Bay

When we first introduced the Florida Bay Coasters in 1988 with the 50' "Florida Bay," we chose a pair of Lehman 120s. These were perfectly sized for the 120,000# Coaster, providing a cruising speed of 8 knots (never did reach predicted 10 knots, though).

When building the 65', 160,000#, "Key Largo," we thought a bit of "extra" HP would be a good thing, so we installed CAT 3208 turbos at 320 HP each. We NEVER used the HP provided for by the turbos - in fact, the most expensive repair was to a turbo due to lack of use. When we did put the hammer down, we dug a hole and blew out a LOT of black smoke. We would have been better advised to use the NA 3208 at 210 HP each.

Over the production life of the Coasters, we installed lightweight Yanmars (still working OK after a single owner of over 20 years), 4 cylinder Fords (rough), 6 cylinder NA Perkins 135 HP (smooth and reliable). As long as we had enough HP to counter head winds (the Coasters have an impressive amount of windage), they were never going to exceed their hull speeds.

Not mentioned in this discussion of over-powering is propping correctly. With a FD hull and a wall at the hull speed, if one over powers, then when running at the real cruising speed, not only is the motor running off its peak performance, but so is the prop. To meet the engine manufacturers requirements, the prop is sized to hold back RPMs at WOT. With a prop sized to an overpowered engine, most likely, the prop will not be as efficient as possible at the cruising speed.

With the advent of modern diesels (read: computer controlled, common-rail or similar electronic injection), it does not hurt the motor to run below optimal RPMs and it will retain fuel efficiency throughout its power curve (except at the lowest and highest RPMs).
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