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Old 03-02-2013, 09:02 AM   #21
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Why do the manufacturers overpower these boats (assuming that the web forum talk is correct)?
Because if the boat has a semi-planing hull, like a GB or your boat, the operator can take advantage of the additional power to go faster albeit at an increased fuel burn.
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Old 03-02-2013, 09:19 AM   #22
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Ron, you put far too much credence in web chatter. Vastly? I'll have to think about that until I finally hear a satisfactory defintion on a trawler. Better yet, pick on KSanders who repowered his trawler with big a$$ twin (yes twins!!) Cummins a few years ago. All he needed were two 40 HP Yanmars, right?
On the contrary, I put verry little credence in web chatter. My point is, either the majority of boat manufacturers don't know what they are doing or the web "experts" are full of BS.

Which do you think it is?
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Old 03-02-2013, 10:29 AM   #23
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On the contrary, I put verry little credence in web chatter.
Then quit chattering.

On a more serious note, the true trawler builders of today seem to have power and hull design pretty well matched. Selene is the notable exception with at least "one size" more (say using a JD1225 rather than a JD 6081) than what is needed. Nordhavn, Dashew, Cape Horn, Northern Marine, Northwest, North Pacific, Diesel Duck, Seahorse, DeFever, Devlin, Seaton, Great Harbor, Watson and half a dozen or so others ae right on target.

The new equalizers of the last decade are engine designs and mandates to fit Euro/EPA emissions requirements. With after coolers, high pressure injection, precise air and fuel metering etc a 375 HP engine can easily perform as if it is only 180 HP -JD 6068 as example.

Marin's dead on point about semi-displacement vessels needing enough oomph to get on plane is probably the crux of your and our chatter. Especially when those owners want to call these vessels trawlers to fit the advertising hype and be able to post on TF (oxymoron).
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Old 03-02-2013, 12:07 PM   #24
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Ron says;

" My point is, either the majority of boat manufacturers don't know what they are doing or the web "experts" are full of BS. Which do you think it is? "

Neither. It's a marketing issue. Wer'e an automotive culture and people use the power to weight judgments based on cars w WAY too much power compared to boats but thev'e got hills to climb. People look at my Willard and think "how on earth is 37hp enough for this 8 ton boat when it wasn't enough for the first VW car" that only weighed 1 ton. Boat manufacturing marketing people bump up the power to sell boats. Yes they know what ther'e doing.

For for full disp boats it's even worse because so little power is needed.
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Old 03-02-2013, 12:32 PM   #25
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I love all or nothing attitudes.....the great roadblock of progress!

I totally agree with manyboats that most trawlers could do with way less...if I repowered now...I may drop to an 80hp or so because of the way I cruise...I know it might hurt resale..but it may help because I know how to market the boat to a smaller but smarter group than the ones that attend boat shows looking to buy...

Didn't Krogen market their 39 footer a few years back with an 80hp something JD but also a bigger engine???? I'd love to see what of each was sold....
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Old 03-02-2013, 03:45 PM   #26
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I saw a 36 GB that had twin 55hp Yanmars and it didn't last long on Yacht World.

For wrench benders w lots of time and not enough money to re power I have a very out of the box idea.

Take the engine or engines apart. Remove half the;
Pistons, rods, push rods, valves ect and basically convert it/them to 3 cyl engines. Choose the correct cylinders to insure a good firing order

Then if you were at 30% loading w 6 cylinders you'd be at 60% loading w 3. And I think 60% is about where I am at 2300rpm. A 60hp GB 32 ... my kind of boat.

Almost no cost but a LOT of work and it's so far out of the box I may not even ever heard of it. Has anybody???
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Old 03-02-2013, 04:04 PM   #27
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I saw a 36 GB that had twin 55hp Yanmars and it didn't last long on Yacht World.

For wrench benders w lots of time and not enough money to re power I have a very out of the box idea.

Take the engine or engines apart. Remove half the;
Pistons, rods, push rods, valves ect and basically convert it/them to 3 cyl engines. Choose the correct cylinders to insure a good firing order

Then if you were at 30% loading w 6 cylinders you'd be at 60% loading w 3. And I think 60% is about where I am at 2300rpm. A 60hp GB 32 ... my kind of boat.

Almost no cost but a LOT of work and it's so far out of the box I may not even ever heard of it. Has anybody???
Sure, cylinder de-activation in all sorts of cars today.
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Old 03-02-2013, 06:25 PM   #28
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For most Displacement boats 1 hp for every 2240 lbs of boat will produce the long range cruise speed most operate at. SL 1 or so.
On the 14-ton Coot, I find its 80-HP diesel (one HP for each 350 pounds) a good combination as the boat can reach hull-speed (7.3 knots) at about 95 percent power.
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Old 03-02-2013, 07:33 PM   #29
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Mark,
Willy is 8 tons and w 40hp. So I'm a little less power per ton than you. You have 5.7hp per ton and I've got 5hp per ton. I don't know if I can reach hull speed or not. Calm water is unobtainium. We average 6.15 knots at 2300 rpm and about 50% load. I could easily do well w 32hp and that would be 4hp per ton. Any lower than that and I'd need a more efficient hull .... more like a sailboat.

Re FFs claim of 1hp per ton I'd be at 10hp or less. As I recall a S/L ratio of 1 would put Willy at a top speed of 5.25 knots. Nowhere near hull speed of 7 knots. My WLL is 27.5'. Did I figure that right?

Tom wrote;
"Sure, cylinder de-activation in all sorts of cars today."
Yea Tom but that's just eliminating combustion on the deactivated cylinders. I want to remove all those unnecessary parts, their weight, and the need to move them as in pistons reciprocating, valves bang'in back and forth ect. BIG difference.
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Old 03-03-2013, 07:36 AM   #30
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"FFs claim of 1hp per ton I'd be at 10hp or less. As I recall a S/L ratio of 1 would put Willy at a top speed of 5.25 knots. Nowhere near hull speed of 7 knots. My WLL is 27.5'. Did I figure that right?"

OOOPS that should read 3HP per ton, not 1.

SL of 1 would give the 5.25L as CRUISE speed , most boats can cruise on the cheap at between .9 and 1.2 times the SL.

A SL of 1.4 is where the bow is up in the air and the stern sunk way down , attempting to climb the boats bow wave, never efficient , usually 3X the fuel burn of SL !.

With 5HP per ton the wave is a bit larger to climb and the fuel burn higher.

Skinney boats do better , round or canoe sterns a bit worse , but all hit the wall of a bow that can not climb up on top.

Now if your boat has 1hp for every 50 lbs , getting on top is a snap, plaining is expensive in HP required tho.

The "semi displacement" folks have enough power to push really hard and some see SL 2 or better but its about SL 3 where plaining starts and for efficient boats the mileage actually gets better.
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Old 03-03-2013, 10:16 AM   #31
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.................... My point is, either the majority of boat manufacturers don't know what they are doing or the web "experts" are full of BS.

Which do you think it is?
For the sarcastic impaired, the answer is, the web "experts" are full of BS. Boat manufacturers have the resourses to select the correct engines and props for the boats they manufacture. Engineers, Naval Architects, computers, test tanks, and actual testing of the first hull.
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Old 03-03-2013, 10:23 AM   #32
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Marketing determines the engine size...

Models with 2 or more different engine sizes will most likely determine what option sizes will be offered in the next model year....Straight from the regional director of marketing for Sea Ray a few years back.

He also explained why a million dollar boat will use a plastic hinge on an access panel in the engine room and not in the galley of many of those expensive boats....
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Old 03-03-2013, 10:55 AM   #33
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For the sarcastic impaired, the answer is, the web "experts" are full of BS. Boat manufacturers have the resourses to select the correct engines and props for the boats they manufacture. Engineers, Naval Architects, computers, test tanks, and actual testing of the first hull.
And from what I've seen new build's are all checked and certified by the engine manufacturers to be sure they meet all the specs. After all, they are the ones carrying the warranty.

But, I do think there is a real over-propping issue in the industry with new boats. Most appear to be propped for a light to medium load which yields a higher top speed than propping for full load. Higher top speed means better glossy brochures, magazine articles, etc. But once the boat is loaded up with all the typical gear, full of water, and full of fuel, it's suddenly over propped. I think this is the issue folks are talking about.
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Old 03-03-2013, 11:18 AM   #34
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For decades and decades every year the new cars had more power. If they didn't have more power they were considered old. We've been brainwashed to think bigger is better and more is better. Just in case you wanna pass five cars just before the curve you may need extra power. Like two or three hundred HP. We're only reasonably comfortable when we've got way too much and after we've had it for 10 minutes it's not enough.

It is the nature of human beings. We are the "takers" of the earth. We never stop taking. Enough is never enough. Basically all other animals on the planet stop taking when they become comfortable ... usually when they have had enough to eat. Not humans.

Reflecting on the above it's not hard to conceive of yachtsmen wanting and buying boats with much more power than could ever be used.

Willy has 5hp per ton. That is actually excessive for a FD boat. Not much but some. With a FD boat the appropriate amount of power is within a very small range. On Willy it's about 30 to 40hp. 24hp would be 3lbs per hp and that would be doable but at a slight loss of speed and no reserve. I question if any reserve is needed and I may actually be able to maintain 6.15 knots using 20 of the 24hp available but even I would like to have 30. And I have 40. Theoretically I have almost twice as much as I've ever needed.

But w a semi-disp hull (over 95% of TF members (those that can exceed hull speed)) the range of power required becomes greater w more speed flexibility. UNLESS the boat is dedicated to noticeably less than hull speed. And if it is the owner would be better off w a FD boat. More seaworthy (especially in following seas) and more fuel efficient .. 50 to 100% less fuel burned. Those w close to planing hulls will benefit most in fuel consumption savings (at approx 100%) and those w hulls close to FD but still semi-disp will gain some.

But w the correct amount of power under loading will almost never happen.

This is all my opinion and have no references to claim.
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Old 03-03-2013, 11:21 AM   #35
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Twisted,

Do you think trawlers will have greater top speed in an over propped condition?

Ron says " the web "experts" are full of BS." Industry, architects, manufacturers, builders and sellers have their customers to answer to. They all need to please the customer first. WE DON"T. Whatever they say or recommend may come back and bite them. I don't have to answer to anybody. I can say what ever I want regarding engineering, design and all that other stuff. If I know the truth/facts I can let it all hang out. So in a way there may be more truth and fact in what a TF member says than someone in the industry. So you could say the industry is full of BS too as their lawyers are controlling what they say.

But you're basically right Ron ... web "experts" are less reliable.
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Old 03-03-2013, 11:35 AM   #36
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But once the boat is loaded up with all the typical gear, full of water, and full of fuel, it's suddenly over propped. I think this is the issue folks are talking about.
XX

My vessel has an empty weight of 50,000 lbs. Fuel and water add about 10,000 lbs with gear, dinghy etc another 2,000- 3,000 lbs. DeFever built 170 DF 48s with mine at #168. The power and weight combination was very refined by hull# 168 with props and engines correctly sized to allow full RPM without overheating. I can do 6 knots with very low fuel burn or speed it up for that beat the tide or climb big swell need.

The "oversized" (by HP rating but not by CID) 225 HP engines are fully capable of being throttled back with no ill effects and will have a very long life as they are not expected to operate in the upper end of the duty cycle. The CID is less than a 25 year old Lehman 6 cylinder.

The blessing and curse of after cooled engines is they yield improved MPG with improved emissions over the RPM range, but with higher maintenance costs. It is unlikely (impossible?) one could buy a new 35 - 60 trawler style boat today without turbos and after cooling. Therein lies the rub with the over propping debate - technology has run well beyond the discussion.

As Twistedtree points out, over propping can brutally harm today's engines. Correct propping in this century is pretty simple or one can make it complicated by their own choice.
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Old 03-03-2013, 11:56 AM   #37
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Twisted,
Do you think trawlers will have greater top speed in an over propped condition?
If by 'Trawler" you mean only displacement speed boats, then No, I don't think so if you keep everything else constant. It might even run a bit slower if the engine can't rev high enough to achieve max HP.

But if you lighten up the boat, it should go faster.

To what ever extend all of us may be talking across each other, it might have to do with displacement operation versus planing operation. Most of the over-propping, burned up engine stories come from planing boats. That's where high output engines appear most often, and is where they get pushed to their limits. I think many exclude planing boats from their definition of a trawler, but I don't.

I also understand the approach of over-propping a displacement boat to achieve some preferred RPM/cruise speed combination even though it may be above the manufacturer's prop load curve. And I think it's fine to do that as long as you also recognize that you've created a situation where at the top end the engine will be overloaded, and that you take measures (like some sort of throttle limit) to prevent operation is that "danger" zone.
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Old 03-03-2013, 12:15 PM   #38
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Twisted wrote;

"you also recognize that you've created a situation where at the top end the engine will be overloaded, and that you take measures (like some sort of throttle limit) to prevent operation is that "danger" zone."

Many people have said as much lately and that understanding of over propping is very important to people that never post on these threads and understand only a little about it. They need to know that it's a little complicated to over prop and the only really safe way is to prop to rated engine speed. They should also know that there is some advantage to over propping on an over powered boat and that there are very few that aren't overpowered.
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Old 03-03-2013, 02:51 PM   #39
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Basically all other animals on the planet stop taking when they become comfortable ... usually when they have had enough to eat. Not humans.
Eric, not to interfere with the post but just a bit of trivia. Did you know that a squirrel or chipmunk collects and hides roughly 12 years worth of food each year of their life as a habit and obviously never finds or eats most of it. One of the park rangers told me this and found it interesting. Deep thoughts!!
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Old 03-03-2013, 05:11 PM   #40
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Well that blew me out of the water.

Seriously hahaha
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