Yamaha Jet Drive?

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From: Da_Nag™ (Original Message) Sent: 8/14/2003 8:31 PM
I was just over at the Yamaha site, and noticed they have jet drive outboards available for 2004, in 40, 60, 90 and 115HP models.

I know absolutely nothing about this technology, other than the marketing speak Yamaha offers up. However, one of their claims caught my eye; they have a jet pump to prop shaft conversion chart that claims a prop shaft 90HP engine is equivalent to a 65HP jet pump engine.

If this claim is true, is there any reason you wouldn't use a jet pump outboard on a C-Dory? One could save over 100lbs. on a main - the F65 Jet Pump outboard only weighs 264 lbs.

Bill

From: LesLampman Sent: 8/15/2003 7:33 AM
Hi Bill,

I don't see any reason a jet outboard wouldn't work on a C-Dory given its bottom configuration but...the horsepower difference actually works against you since you lose about 30% of the rated horsepower with a jet pump. Than means to get 50 hp (at the pump) on the back of a CD16 we'd have to use a 75 hp outboard...way too much weight on the CD16; you'd have to put an F115 on your CD19 to have 80 hp at the jet. The jet drive lower unit (and they're all made in San Leandro by Specialty Manufacturing) does weigh less than a standard lower unit but not that much. The lower unit of an F75/80/90/100 or BF75/90 weighs in around 30 pounds and the jet lower unit maybe half of that so the net savings in weight is only aound 15 to 20 pounds. I don't know where the 100 pound figure comes from; even the on the BF225 the lower unit assembly doesn't weigh that much (maybe 60 pounds).

Les

From: Da_Nag™ Sent: 8/15/2003 9:45 AM
Hey Les,

Duh - never mind. The chart provided at the link above was not very clear, at least to me initially. Add to that my ignorance regarding the relative inefficiency of a jet drives, and we end up with a recipe for a dumb question.

For example, I thought it was saying a 90HP prop motor was equivalent to a 65HP Jet pump motor - that's where I was getting the 100+ lb. difference, by looking up the weight of the 65HP motor and comparing it to a 90.

However, after reading your note and re-reading the chart and specs, it became clear what they're really saying. They're not comparing different prop and jet drive motors; they're saying their 90HP engine puts out 65HP at the pump.

Which, as you pointed out, ain't a good thing as far as weight is concerned...

Bill

From: Mike Sent: 8/15/2003 2:19 PM
Besides that, those jet pumps sound like a busted lawnmower.

From: Redƒox Sent: 8/15/2003 4:15 PM
Yeah I hear the things will wear out your motor faster than anything, the engine always has to be at a pretty high rpm just to get out of it's own way!