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Old 11-19-2012, 06:49 PM   #1
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Over Powered Boats

according to the calculator i used Boat Speed Calculator

the boat i was interested is over powered by a factor of 2. This boat has twin 130's and the max power needed to reach hull speed of a 41 defever 29000 lb boat is 143hp. There are lots out there with twin 22o's and i wonder what advantage that gives them besides more frequent fueling stops?
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Old 11-19-2012, 07:18 PM   #2
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hulll speed on one engine (plus the additional loss of efficiency by being on one engine)??

As a single guy, the second engine and around 50hp on the other one is all a waste in my mind...but that's just me...
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Old 11-19-2012, 07:35 PM   #3
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Greetings,
I need 128 HP to get 9.1 knts hull speed. I am over powered X2 as well. "Advantage"? Those are the numbers that came with the boat and I really don't care what fuel usage is. Fuel cost is such a minor expense when you compare it to marina fees, insurance, maintenance upkeep and repairs etc. I don't worry about it at all. Further more, the boat I run was never offered with a single.
A particular vessel may use 4gph over a 200 hour season (average season I would say is 100hrs) versus one using 2gph. @ $4/gal that works out to be in the $1600 range. Hell, that would barely pay a family of four's weekly admission to Disneyland NOT including food, transportation and accommodations!
I am by no means wealthy nor do I have a particularly new or economical boat but she is what she is.
Now Mr. 4445 you are in a unique position where you can buy what you want which is built where you want.
Happy hunting.
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Old 11-19-2012, 08:08 PM   #4
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Greetings,
I need 128 HP to get 9.1 knts hull speed. I am over powered X2 as well. "Advantage"? Those are the numbers that came with the boat and I really don't care what fuel usage is. Fuel cost is such a minor expense when you compare it to marina fees, insurance, maintenance upkeep and repairs etc. I don't worry about it at all. Further more, the boat I run was never offered with a single.
A particular vessel may use 4gph over a 200 hour season (average season I would say is 100hrs) versus one using 2gph. @ $4/gal that works out to be in the $1600 range. Hell, that would barely pay a family of four's weekly admission to Disneyland NOT including food, transportation and accommodations!
I am by no means wealthy nor do I have a particularly new or economical boat but she is what she is.
Now Mr. 4445 you are in a unique position where you can buy what you want which is built where you want.
Happy hunting.
well said. all things considered like the initial cost of a boat insurance marina fees etc. the fuel is not much.
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Old 11-19-2012, 08:56 PM   #5
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Increase that to 500-1000 hours a year at 4 gph versus 2 gph and that's $4000-$8000 (@ $4/GALLON)...still not huge but a dent in a fixed income cruisers budget.
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Old 11-19-2012, 09:08 PM   #6
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I'm not sure how applicable that set of tables is to my boat. It calculates my hull speed at 12.89kts which I think is on the high side. At that speed my stern is digging in and I'm really plowing. A more efficient speed for my boat is around 10kts.

Using his figures it says my boat could reach that 12.89 kts with 314hp. I don't doubt that, but there's no calculation to determine what the proper horsepower would be to get my boat on plane.

At WOT (2150rpm's) I'm running at 30.3 kts (light load) and at 80% throttle (1750 rpm's) I'm cruising easily at 22-24kts (depending on load).
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Old 11-19-2012, 09:14 PM   #7
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Fill'er up for the seven-knot Coot is about $1200 (300+ gallons). Lasts about a year although usually purchase $400 at a time. Fuel is only a fraction of berthing, or insurance, or maintenance, or property-tax costs, individually. Nevertheless, that's better than if fuel costs were more than everything else.
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Old 11-19-2012, 09:22 PM   #8
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Almost all trawlers represented on this forum are overpowered. That is unless you go forth as Marin does. Over hull speed and running his engines at about 55% load (minimum in my opinion).

Hull speed is almost always misunderstood among trawler skippers. With a semi-disp hull the actual boat has to be taken into consideration to contemplate a good cruising speed. Full disp hulls should run about one knot BELOW hull speed for good economy and to be not overdriving the hull. SD hulls like a GB to an IG would best be run at about hull speed to very slightly over w the IG that has a more planing hull. Or faster if you like and can afford.

If you want to cruise at 7 knots in your GB 36 you should be looking for a single engine boat. Or a 36 that has 2 50 to 75hp engines.

The problem is that these boats were marketed during a period of good economic times and cheap fuel. Fuel consumption even now is not the concern of those that buy new boats but a 25 to 35 yr old boat bought w a fraction of the money required for a new one will have owners that have a hard time paying for all the expenses planed for much less the fuel on top of all the other stuff so we find old trawler owners running their boats at 7 knots. And almost ALL of their boats have at least 2 times as much power as they need. Many think (incorrectly) that they need a lot of extra power to run and hide from weather but it doesn't play out.

There's only a few FD boats on this forum and 3 to 5 hp per ton is plenty of power. I'm talking total power not just what will be needed for cruising. My Willard 30 for example has 40hp total and uses about exactly 20hp to cruise at 1 knot below hull speed (6.15 knots). A 40' Willard would require about 25hp to cruise and (w it's greater windage) about 60hp total.

Semi-disp (SD) hulls are more difficult to call as many are almost FD hulls and others are almost full planing hulls. A rule of thumb could be to say they should require about half as much power as they came with. That would get you close in most cases. But you could be way off w others. Comparing similar boats can lead you quickly to the answers but you need to be able to determine what percentage of total power is being used and what that power is. About the only way to figure it out is to know the WOT fuel burn at the rated rpm. Say it's 6 gal per hour. If you burn 3 gph at 2000rpm you will know you are at 50% load at that rpm. And w a 120hp engine that equates to 60hp.

If you can find a cheap boat w a bad engine you have the opportunity to create a boat that is not overpowered. Otherwise w what's available on the market you'll just have to buy an overpowered boat live w it.
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Old 11-19-2012, 09:33 PM   #9
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Several advantages
Around my cruising area we have currents to fight
Getting an extra 2 kn's can mean the diffence between making a tide ,or waiting 3 or more hr's for the tide to slack off or change

It's also nice to get a little extra speed up to beat a friends boat into a slip ,anchorage,(or if you push it a lot) into the fuel dock as you will take longer to fill up lol
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Old 11-19-2012, 10:16 PM   #10
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I really enjoy piloting my boat and don't care much about getting somewhere other than the next anchorage, which for me is usually 6-8 hrs. away. Someone here on TF reminded me that my GPH had to be compared with my FPH (fun per hour). When I realized that my fun consumed only 2.2 GPH at 7.5 knots with my gennie running, I figured that my fuel cost for that was about 10 bucks per hour. What fun can you have these days at 10 bucks per hour?

If I was on Interstate 95, I could fight my way to average 60 miles in an hour, costing 12 bucks or so at 20 MPG. Heck, I'd give you the 12 bucks for the fuel and another 12 bucks on top of it just not to do it.

Regarding the topic, the original half dozen of the Krogen Manatees had a 50 hp Perkins that drove the hull easily at 6.5 knots. After that initial offering, they changed the standard engine to 90 HP Volvos.....then 100 HP, and I believe the last one may have had a 110 hp, all Volvos. The Volvos were all able to get 7.5 knots comfortably, and Jim Krogen said that he could get 8.5 knots WOT with his 90 HP version in 10 ft. or so of depth, turning the original 13 X 22 wheel. I've got a 140 HP refit Yanmar in mine, and my economy numbers match the Volvo very closely, but the 40 HP or more is a waste of engine that I never use. The boat will begin to dig a hole at 9 knots that it wouldn't come out of with 500 HP. Yes, we see our boats at 12.5 knots or so (especially in a following sea) but if you turn the boat around without touching the throttle position, you'll quickly learn that adding both speeds and dividing by two gets you back to the same old realistic numbers. Now that a few of these boats are being refit with somewhat higher HP engines, competitive Manatee performance (I mean does that sound ridiculous or what) will have to be measured not in speed, but which boat can did the biggest hole. There's another Manatee here in Miami with a new 160 HP Volvo, installed by an insurance settlement. Sometimes I go cruising by his place juicing my Yanmar, but nobody ever comes out. Both of us know that the big boys will eventually have to settle this "hole" thing once and for all.

If you opt for twins in a full displacement hull, enjoy the handling advantages and redundant benefits of the boat. Higher speeds will only be possible with semi-planing or planing hulls, or perhaps a power-catamaran if you choose. If you end up with a single that has a HP rating that is more aligned with the hull capabilities, enjoy the simplicity and economic benefits of that feature. Your aim should be FPH (fun per hr.).
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Old 11-19-2012, 10:30 PM   #11
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I really enjoy piloting my boat and don't care much about getting somewhere other than the next anchorage.....~~ Your aim should be FPH (fun per hr.).
Preach it brother!!

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Old 11-19-2012, 10:49 PM   #12
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your thoughts say pretty much what my calculations have taught me. I've never been into wasting a non renewable resource unneccessarily even back when fuel was 35 cents per gallon. I always had a desire to save some for future generations.
Seems to me that with the proper engine of modern design naturally aspirated of course a 40 foot DeFever style vessel should not use more than 2gph max. Last year i had Wooldridge build me a little beer can craft with a 115hp 4stroke merc. This engine dosent seem to use any fuel to speak of and it certainly uses less than the 9.9 kicker i also bought for this boat. The new engine control systems used on this design are incredible. The monitoring system< smart craft is the name i think> even tells you when you are at the most economical speed for the current engine load and measures exactly how much fuel is used. Wish i could equip a trawler with this kind of system.
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Old 11-19-2012, 11:15 PM   #13
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bfloyd4445,
If you want 2 gph and a 40' boat you need a full disp boat. Like a Krogen 42 or a Willard 40.
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Old 11-19-2012, 11:49 PM   #14
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Almost all trawlers represented on this forum are overpowered. ......If you want to cruise at 7 knots in your GB 36 you should be looking for a single engine boat. Or a 36 that has 2 50 to 75hp engines.
I think Eric is right on the money with his whole post. If hull speed (or preferably slightly below hull speed) is what you want for maximum economy then one engine in a boat like a GB36 is the way to go. A smaller engine than even the FL120 would make more sense if maximum economy is what's desired.

But as Eric points out, these boats were made at a time when fuel was cheap and buyers wanted the ability to get to their destinations, or their cruising grounds, quickly. More power enabled them to do that, so that's what American Marine/Grand Banks gave them, to the point where at the end of its production run the stock engines in a GB42 were a pair of 400-something hp Cats. The boat will do 15-16 knots all day but the total fuel burn is in the neighborhood of 23 gph.

Even today, with diesel in the $4 per gallon range, I see GBs in the islands running at 12-15 knots. The hulls can do it, so if you have the power and the wallet, why not take advantage of it?

We run our engines in the ideal power range for the FL120 if the goal is maximum engine life. That gives us a cruise speed a bit over hull speed but not much. If our boat had more powerful engines that could take harder running we would cruise our boat two knots faster than we do now, or more if we could get it without over-stressing the engines.

There is a remote possibiliy we may repower our boat in the next year or so. If we do, we will go with engines that are at least 150hp but more likely will be in the 200-250 hp range. This should enable us to cruise at 10-12 knots with a reasonable fuel burn.

That's still way too slow for our taste, but as Eric says, you use what you got.

So if you want a GB or an IG or just about any of the diesel cruisers we're talking about here, a single engine version will get you the best economy if you are willing to creep along at just below hull speed. So 6 knots or so in a GB36. That single-engine GB36 will still be "overpowered" for that kind of cruising but unless you're willing to cough up the bucks for a repower you'll just have to live with the 'too-big" engine the manufacturer put in the boat to begin with.
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Old 11-20-2012, 12:04 AM   #15
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... So 6 knots or so in a GB36. That single-engine GB36 will still be "overpowered" for that kind of cruising but unless you're willing to cough up the bucks for a repower you'll just have to live with the 'too-big" engine the manufacturer put in the boat to begin with.
Six knots seems fast to this former sailor:

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Old 11-20-2012, 06:58 AM   #16
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"and i wonder what advantage that gives them besides more frequent fueling stops?

The "advantage" was not for YOU!"

The advantage was in the initial engine price for the boat assembler.

That's the sales technique for Volvo, and low cost was the selling point for Ford Econo Power and many other marinizers.

The first purchaser though the low price was great , and YOU get to live with his choice.
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Old 11-20-2012, 07:09 AM   #17
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Any of the mid sized trawlers can be a 2gph boat...it's called "throttle management"...

Many have reported that at 2gph, many of the Taiwan trawlers go around 7 knots thus 3.5 NMPG plus or minus.

My personal goal is 4NMPG for planning purposes. I'm willing to accept the 6-6.5 knot cruising speed it will take to get 4NMPG.
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Old 11-20-2012, 09:37 AM   #18
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Mark,
Looks like you're going 8 knots in the pic.

Marin,
Hull speed is NOT the best speed for economy. Hull speed has most to do w wave length and it's effect on boats underway. Until one gets to or close to idle speed the name of the game is "the slower the better". One knot under hull speed on a semi-disp hull won't get as much economy increase as a FD hull would but there would still be much reduced fuel burn. I burn 1gph at 6 knots and would prolly burn half that at 5 knots ... or at least very close to it.
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Old 11-20-2012, 10:01 AM   #19
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bfloyd

The cheapest way to boat is stay at the dock, many do. Or as suggested throttle back. If you really want to be a guy to save a non renewable ( with ever more being found for the rest of us) resource don't buy a boat. Fortunately the boating lifestyle me and my great grandchildren will enjoy is fueled by a world awash in oil. If you search carefully you can find a 40DF with a single. For fishing around Coos Bay the various Tollycraft diesels and gassers are great choices plus provide you the 15 + knot opportunity to get out of the weather and hit the bar crossings at the right time.

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If you had the time, money and desire what blue water PROVEN capable vessel, less than 65' would you buy? Assuming too you wanted an engine for get home power. I'll help you look for one at the upcoming Seattle boat show.
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Old 11-20-2012, 10:49 AM   #20
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Several advantages
Around my cruising area we have currents to fight. Getting an extra 2 kns can mean the diffence between making a tide ,or waiting 3 or more hr's for the tide to slack off or change

It's also nice to get a little extra speed up to beat a friends boat into a slip ,anchorage,(or if you push it a lot) into the fuel dock as you will take longer to fill up lol
Stray Cat, we have a similar problem here. Current flow on the Columbia in the spring can be as high as 4+kts. That's great when you're running downstream and trying to make it to the next lock. It's not so great when you're running upstream to the next lock.

The dams on the Columbia vary from about 25 miles apart (Bonneville to The Dalles) to 75 miles apart (John Day to McNary). When you're on the summer schedule and you need to make it to a lock in a set amount of time, running against the current can really foul your plans. It's relatively easy to do the 25 mile distance in the 3 hours between scheduled lockages. When you're trying to do the 75 miles in 6 hours and running against a 4kt current, that makes it a bit tougher.

That's when the availability of extra power is nice.
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