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Author Topic:   Jet drive outboard/13-foot classic
ancient1 posted 09-30-2004 01:04 AM ET (US)   Profile for ancient1  
I'm thinking of repowering with a Yamaha 40hp jet drive on the old 13 footer. The boat's still in great shape, but the old Johnson is shot.

Does anyone have any experience with jets on a 13?

HuronBob posted 09-30-2004 09:03 AM ET (US)     Profile for HuronBob    
According to Yamaha's web site, a 40 hp jet translates to a 30 hp prop drive... you'll be losing some power!

Although I've never had an outboard jet drive, my one experience with an inboard jet only lasted a year.. I got tired of intakes clogged with weeds..... it was great on the open lakes, but a huge weed sucker on the skinny waters....

But, I'm guessing you've already considered these factors....


Dick posted 09-30-2004 07:38 PM ET (US)     Profile for Dick  Send Email to Dick     
I ran jet drives, both outboard and inboard in Alaska for years. The secret to keeping a clean intake is RPM. If you keep the RPM up the weeds will suck through and the pump will act as a garbage grinder. Drop to an idle in shallow water and expect a clog.


AQUANUT posted 09-30-2004 10:32 PM ET (US)     Profile for AQUANUT  Send Email to AQUANUT     
Its my job to convert yamahas/mercurys/hondas/johnson and evinrudes from props to out board jets..I do it often,
from 25 hp to 225 hp.

a jet outboard is neccessary in some circumstances and boating environments. as a rule, figure 33% horsepower loss from a proped outboard converted to jet, along with that, consider a loss of fuel economy. its a known fact.

However, in certain rivers with strong flows and shallo depths, there is no option except for a jet.

if you were asking, how a 200hp mercury would perform with a san leandro jet pump installed, well there is alot of ponies to play with so whats the impacy of 66 of them going away?

the impact is greater on the smaller hp engines, [more noticable], nonetheless 33% hp reduction.

one more point, if you are considering a jet outboard,
the throttle response seem to be a little slower on the 4 stroke versus 2 stroke, a key issue for metal hulled river boats, this is to be expected. due to the throttle on tiller drive models only..the contorl box models it appears tp be the same.

PeteB88 posted 10-04-2004 11:48 AM ET (US)     Profile for PeteB88  Send Email to PeteB88     
Intersting idea but there really is no reason unless you are running rivers and there are shallow areas that might become a problem for propellers. Props are more efficient anyway. If underwater hazards are an issue there are prop guards that are somewhat effective however damage to lower units is very possible.

If you want a jet drive then I would say get a boat hull/power combo designed for that purpose. If you need the ability to navigate rivers with hazards where jets work best then get an aluminum jet boat - aka jet sled designed to do the job. They are heavy built, bomb proof bottoms designed to take direct impact on rocks and bottoms w/o puncturing the bottoms. I cannot image running a Whaler or any glass boat in such conditions although I know in New Zealand and some whitewater areas there are specific designs for this purpose.

Whitewater jets are interesting and great boats. Most of the PNW manufacturers are good companies with fascinating histories.

Finally, the loss of HP is a very significant issue.

captbone posted 10-04-2004 08:36 PM ET (US)     Profile for captbone  Send Email to captbone     
I really see no major improvement over a 40hp with a gear case unless you have alot of rocks. You will loss performance and economy to gain only inches. A 40hp prop with a jackplate and power trim and tilt can get you into less than a foot of water if you keep it on a plane. I can not see a jet drive getting you anymore that 3-4inch better on the draft. Just my 2 cents

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