Arild Wholeheartedly agree with your premise. I would estimate that it takes no more than 100 HP to move this boat through the water at 8 knots, a 48 Ft Gulf Commander. I would further submit that a single 120 HP diesel engine would be more than sufficient. A more contrary position would be concern about tides, narrows and such on the west coast; however, there are owners out there with low powered boats taking these issues in stride and travelling accordingly. I would also say that a 20 ton boat with twin 3160 cats @ 210 HP does dig a fair hole when using full power, but being a semi-displacement hull the hole is not as big. However, in support of the overpowering industry that appears to be prevalent, gas was much cheaper back in the late sixties, early seventees. Another issue, slightly off topic is finding an older boat, say '70s vintage with a sizeable BW tank (grey water soon to be uppon us). Saying all this, is it better to repower with less horsepower, considering the possibility of changing transmissions and other anciliaries, or just rebuilding the same and cruising accordingly? Ernest On Mon, 21 May 2007 11:17:18 -0700, "Arild Jensen" <elnav@telus.net> wrote : > > > > -----Original Message----- > > From: Ernest Nash > > Looking for information/opinions regarding 3160 Cat diesels, > > > > Repowering - replace with lower power diesels with newer technology or > > rebuild, the 210 HP out of these Cats apparently can take the boat to 15 > > knots, hardly up on plane but drinking a lot of gas. Taking a boat this > > size past 8-9 knots is not fuel efficient in any way. Opinions? > > Ernest Nash > > > REPLY > In light of current and forseeable fuel pricing, the topic of how much power > is really needed to move a given boat hull is going to get a lot more > attention. > Does it make any sense to have twice as much horse power installed than what > is required to drive the hull at an economical hull speed? > I'm not talking about having some reserve to deal with contrary head winds > and maybe a bit of opposing water current. > I'm talking about the habit by marketing people to use numbers and the > bigger the better. A trend which often leads to ridiculous horse power > ratings far beyond what can reasonably be used on that boat. > Naval architects have reliable formulas backed up with tank testing that > show exactly how much power is required to move a given hull at a specified > speed. In the case of a true full displacement hull, we know exactly how > fast that hull can move at maximum speed. > > A number of listees have mentioned they seldom if ever run at maximum > throttle because of the excessive fuel burn that produces. Evidently these > boats were built with oversized engines. > Engines that can be delivered in varying HP sizes have much longer life > expectancy in the lower power range than when maximum power is extracted. > > Seems to me the whole boating industry is due for a reality check when it > comes to determining engine horse power for a given hull size. Trawlers in > particular do not benefit from over powering the boat. They simply dig > bigger holes in the water and tend to empty the owner's wallet faster. > > What say the list members? > > Arild

> -----Original Message----- > From: Ernest > Saying all this, is it better to repower with less horsepower, > considering the possibility of changing transmissions and other anciliaries, or just > rebuilding the same and cruising accordingly? REPLY If the existing transmission cannot bolt up to a smaller engine, there will probably still be a resale value to offset getting a gearbox to match. As another poster said, such a repower will definitely enhance resale value. Selecting an engine that can drive the hull at full displacement speed with a 20% reserve should be less expensive. Concerning other anciliaries; they would be larger than required but this should not be a detriment. Cheers Arild