Fuel Economy - Weight and Horse Power

[nowornever]

I will be guying a new four stroke for my 5.2 Meter Viking. I have looked at the sea trials at Seamedia website and the 115 Yamaha gets about 15 liters per hour, in a boat about the same weight as my boat.

I have looked at sea trails of the 140 Suzuki but the boats are alot heavier than mine, and they get around the 22 per hour.

My question is, is it the weight or just the Horse power that makes it chew 22 per hour. My boat is a old model 5.2 Seafarer which isnt that heavy I think, not sure its about 700 kilo. So because my boat is so light, with the 140 would I get 22 per hour or more about the 15 ???? If I go for the 140, or should I stay with a 115 to get the fuel economy?

[John_R]

What is the HP range and the max transom weight on the boat from the Manufacturer? Should be on a plate on the boat somewhere.

I have a Quintrex 530 spirit that has 90-115 for HP and 220kg for max transom weight.

I put a Johnson (Suzuki) 115 4 stroke on it that weighs 189kg. I think it gets about 16 L/hr at 4000.

[nowornever]

What is the HP range and the max transom weight on the boat from the Manufacturer? Should be on a plate on the boat somewhere.

I have a Quintrex 530 spirit that has 90-115 for HP and 220kg for max transom weight.

I put a Johnson (Suzuki) 115 4 stroke on it that weighs 189kg. I think it gets about 16 L/hr at 4000.My boat is old, 80 model I think, it seez max hP 175 but thats the old horse power at the prop.

But then in those days it would have been a very heavy motor.

[Noelm]

there is a lot of variables that come into it as well, but those figures seem about right, the old "it is doing the work easier" with a big Motor does hold some truth, BUT it is still bigger and needs X amount of Fuel to make it go, so it is not as clear cut as we might think.

[Outsider1]

My boat is old, 80 model I think, it seez max hP 175 but thats the old horse power at the prop.

But then in those days it would have been a very heavy motor.

Not really nowornever. My old Johnson 150hp 2stroke weighed 167kg, the 175hp was the same motor and would have weighed almost the same. The 115hp Yammy you are considering weighs 188kg and the Suzuki 140hp weighs 186kgs. The old carby 2 strokes were very light motors comparatively to today's 4 strokes.

You should check the weight maximum for your hull, if only to make sure you don't void your insurance. Having said that I don't think you will have a problem with the boat floating either of the motors you are considering.

What motor is on it now? That might also offer a guide to current weight on the transom, and what sort of performance you are used to?.

My personal view is go the Suzuki 140hp; it weighs the same as the Yammy, has a great reputation and is actually cheaper than Yammy as well. The difference in fuel consumption will be negligible in the scheme of things (the difference in purchase price is more significant in my opinion). And finally that little bit extra horsepower will mean your motor will work that little bit easier in all situations and you will love the power on tap when you need. Some reckon the Suzy only makes 128hp, I am not sure on that, but that is still 10% more than the Yammy.

If you want an another opinion give Peter Webster (Editor) at F & B mag a call. He will know your boat well and is a great fan of the Suzy 140hp.

Cheers

Dave

[PADDLES]

just remember the old "energy cannot be created or destroyed" theory mate. it's efficiency that you want to be looking at, ie. energy losses for a given amount of output. i think you will find that both the yammy and the sooz 4s motors will have fairly similar efficiency and as such will probably chew about the same amount of juice if set up correctly on your boat. (setting up correctly meaning propped right and positioned to run as efficiently as possible).

there are way too many other contributing factors to be able to accurately compare different motors on different hulls.

[Noelm]

back when I used to fit/sell Motors for that Boat, the best suited Motor was the old 2 stroke 115HP (we sold Johnson) fitted lots with that combo, also some with bigger as well even one with the max 175HP and a lot with twin 55hp's but the 115 was by far the best all rounder, the 90 was still popular and went OK, so I guess that only added confusion for you, but be careful of the weight factor, the old Viking is not known for it's overly high transom setup (but heaps better than the Vsea)

[Noelm]

by the way, what has it got now? and if it is still in operation, just for fun, work out the weight needed to make up for each new Motor you are intersted in, and do the old "sandbag" trick to add the weight when the Boat is in the Water, but make sure you test it with a couple of Blokes in one corner at the rear to get a true indication of a Fishing situation!

[FNQCairns]

If possible look past the L/H and at distance traveled per crankshaft revolution. For instance if the 140 allows you on your light boat to push a pitch of prop that is say 2 higher than another 115hp engine (per crank revolution) thats efficiency in the bank as the distance you can travel p/h at this greater cruise speed equates to less fuel used to get there due to a faster time, the faster you can cruise the more the hull lifts and therefore less drag, of coarse it's usually the hull that decides the cruise speed for conditions so lot's of give and take in the real world.

Cheers fnq