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Author Topic:   Engine Weight On Light Boats

NJCoastFlyFish posted 08-06-2006 12:43 PM ET (US)
I just read Jimh's post [which one?] and it got be thinking about my future re-power. I have the 16ft 7in hull (1966) which is a fairly light hull and I'm thinking a four stroke might not be the way to go. My thought is 40% fuel savings is pretty good, but wouldn't the extra 100-lbs of outboard in the stern make the boat handle badly and cause that 40% to be more like 30% or 20%?
I'm looking for someone with a 90-HP two-stroke Yamaha on the back of a 16-foot hull to tell me how much fuel they use on an average trip. I'm also looking for someone with a 90-HP four-stroke (include make) to tell me how much fuel they use on an average trip.
Please include miles in the trip and number of people on board and weight as well as your average cruising speed and any other variabled that must be accounted for.
Almost forget, this comparason is only for the 16ft-7in hull, and please tell what model you have.
gabollini posted 08-06-2006 03:24 PM ET (US)
I've also got a similar concern with my 1988 15'3" sport. I either go with a two-stroke Yamaha 70, sacrifice 10-HP and get a 60-HP four-stroke Yamaha or Mercury, or an E-TEC at about 20-lbs more. With a light, 550-lb boat like a SPORT 15, 20-lbs and 10-HP less is consideration.
bluemarlin posted 08-08-2006 12:18 AM ET (US)
I had a 1988 15 Sport with a Yamaha 50 four Stroke. ( I believe it is exactly the same weight as the 60) I had a day this July when I filled up after fishing a long day in Baja Mexico. Seventy-three miles GPS on 11-gallons of fuel. Roughly 17 miles were up and running (around 20-knots) and the other miles were trolling 8-knots for dorado, billfish, and tuna. This was a 2000 caburetor four-stroke. It was amazing. Unfortunately that motor was destroyed when the boat was flipped at its mooring in a middle of the night Chubasco (70 mile per hour wind). Prior to this motor I had an older carburetor two-stroke Mercury which I couldn't carry enough gas on the boat to go 73 miles.
jimh posted 08-08-2006 09:17 AM ET (US)
The engine weight is an important consideration on a small boat, where the hull weight is relatively light in relation to the engine weight. It is fortunate that the classic Boston Whaler boats have a great deal of stability and reserve buoyancy, and they often can carry a heavier engine better than most older boats of their size. But you should consider the engine weight and its effect on the boat's handling. Some of these modern engines are significantly heavier than the classic two-stroke outboards for which the hulls were originally designed.
Weight always carries a penalty in performance. The more weight in a boat, the slower it goes, and the worse the fuel economy. The secret to good fuel economy and performance is to have a high power to weight ratio. Again, we are fortunate that classic Boston Whaler boat hulls are quite light for their size. But modern motors have become rather heavy.
I think in the future all outboard manufacturers will be trying to reduce the weight of their motors where possible. This will be a difficult engineering project, as the motors are already made mainly from aluminum, so there is no simple way to make a big change. They'll have to find a lot of little weight savings to reduce the total weight.
One of the reasons the four-stroke motors weigh more is they just have more components. They are more complex motors and have many more parts than a classic two-stroke outboard. That is why they cost more, too.

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Author	Topic: Engine Weight On Light Boats
NJCoastFlyFish	posted 08-06-2006 12:43 PM ET (US) I just read Jimh's post [which one?] and it got be thinking about my future re-power. I have the 16ft 7in hull (1966) which is a fairly light hull and I'm thinking a four stroke might not be the way to go. My thought is 40% fuel savings is pretty good, but wouldn't the extra 100-lbs of outboard in the stern make the boat handle badly and cause that 40% to be more like 30% or 20%? I'm looking for someone with a 90-HP two-stroke Yamaha on the back of a 16-foot hull to tell me how much fuel they use on an average trip. I'm also looking for someone with a 90-HP four-stroke (include make) to tell me how much fuel they use on an average trip. Please include miles in the trip and number of people on board and weight as well as your average cruising speed and any other variabled that must be accounted for. Almost forget, this comparason is only for the 16ft-7in hull, and please tell what model you have.
gabollini	posted 08-06-2006 03:24 PM ET (US) I've also got a similar concern with my 1988 15'3" sport. I either go with a two-stroke Yamaha 70, sacrifice 10-HP and get a 60-HP four-stroke Yamaha or Mercury, or an E-TEC at about 20-lbs more. With a light, 550-lb boat like a SPORT 15, 20-lbs and 10-HP less is consideration.
bluemarlin	posted 08-08-2006 12:18 AM ET (US) I had a 1988 15 Sport with a Yamaha 50 four Stroke. ( I believe it is exactly the same weight as the 60) I had a day this July when I filled up after fishing a long day in Baja Mexico. Seventy-three miles GPS on 11-gallons of fuel. Roughly 17 miles were up and running (around 20-knots) and the other miles were trolling 8-knots for dorado, billfish, and tuna. This was a 2000 caburetor four-stroke. It was amazing. Unfortunately that motor was destroyed when the boat was flipped at its mooring in a middle of the night Chubasco (70 mile per hour wind). Prior to this motor I had an older carburetor two-stroke Mercury which I couldn't carry enough gas on the boat to go 73 miles.
jimh	posted 08-08-2006 09:17 AM ET (US) The engine weight is an important consideration on a small boat, where the hull weight is relatively light in relation to the engine weight. It is fortunate that the classic Boston Whaler boats have a great deal of stability and reserve buoyancy, and they often can carry a heavier engine better than most older boats of their size. But you should consider the engine weight and its effect on the boat's handling. Some of these modern engines are significantly heavier than the classic two-stroke outboards for which the hulls were originally designed. Weight always carries a penalty in performance. The more weight in a boat, the slower it goes, and the worse the fuel economy. The secret to good fuel economy and performance is to have a high power to weight ratio. Again, we are fortunate that classic Boston Whaler boat hulls are quite light for their size. But modern motors have become rather heavy. I think in the future all outboard manufacturers will be trying to reduce the weight of their motors where possible. This will be a difficult engineering project, as the motors are already made mainly from aluminum, so there is no simple way to make a big change. They'll have to find a lot of little weight savings to reduce the total weight. One of the reasons the four-stroke motors weigh more is they just have more components. They are more complex motors and have many more parts than a classic two-stroke outboard. That is why they cost more, too.