Yamaha 8hp 2 stroke prop recommendation

[anamealreadyinuse]

I have a 1997-1998 8 HP Yamaha 2 stroke that has the standard prop that came with the motor (see attached). The prop has its fair share of dings and scars but serves us well puttering around in our J16.

I found the tutorial on props but if failed to say how Pitch affects what I'm after? The props on iboats looks like Pitch is the biggest differences in this motor? What would you recommend and why?

http://boatpropellers.iboats.com/Yamaha/8_HP_(1986-2009)_Propellers/381/?*******=057414271

I was told if I upgraded my prop that it could help get me a little more power/speed and possibly plane our barebones J16 in conjunction with a hydrofoil.

I'd like to stick with an aluminum if possible as I imagine its more affordable and I know from experience can take a whack or two. How do I determine what prop to purchase? I know there are all sorts of angles and such and I have no idea. Any advice?

 

[steelespike]

Re: Yamaha 8hp 2 stroke prop recommendation

We need your prop size.it may be near the base of the blades or under the prop nut.
Size is always written diameter X pitch. I'd like yo try it without the foil. A 8 hp can make speeds around 17 mph on a
light reasonably fast boat.
Your 16 foot bare bones boat may actually be an advantage. The bigger foot print will help it get up on the water and the length wqill help keep the bow down as you accelerate.
I suspect it may be a jon boat,the flat bottom should also help it get up on the water.Unfortunately it probably has many keels
on the bottom probably not the best for speed.
Weight distribution is important some times you may want some one in the bow to get planed off
then they may be able to move back.
Very basically decreasing pitch (lower numbers) increases power and rpm,increasing pitch lowers power and rpm but may add speed if the motor can get up to operating rpm.

 

[anamealreadyinuse]

Re: Yamaha 8hp 2 stroke prop recommendation

17 is all I need, its actually more than enough for what we use it for. I have a 8 and 1/2 by 7 1/2 (order the #'s appear on the prop) ... should I look to decrease to a 7 pitch to give myself more power?

 

[Sea Rider]

Re: Yamaha 8hp 2 stroke prop recommendation

The worst prop investment is to buy a new one without even having rpm tested the current one in use. Is a J16 a sailboat as in J24 ? With current prop and load must install a induction tach and check max rpm achieved at wot to determine if inside safe rpm working parameters. A 8HP is a limited engine, don't expect a power burst just boat-engine optimization.

Happy Boating

 

[steelespike]

Re: Yamaha 8hp 2 stroke prop recommendation

Ok 7.5 "pitch.To do this right we need your present wot rpm and gps speed.
I forgot to mention that decreasing pitch will increase power and rpm but increasing speed would depend on the previous props performance. If the motor is below recommended wot rpm increasing rpm should increase speed and should improve hole shot and probably in your case the ability to plane.
For now your present lightly loaded wot speed will be a good start.For it to be relevant the boat needs to plane.
If it struggles try different trim settings,move the tank forward. Maybe a light passengher in the bow till it planes then move back a little.
If your really heavy you may need a tiller extension so you can sit farther forward.

 

[anamealreadyinuse]

Re: Yamaha 8hp 2 stroke prop recommendation

J16 is a Carolina Skiff kit series. The boat come with just the hull and you build it out. I have just a rear seat installed. LOA is 15'8" and Beam is 64", Hull weight is 330lbs. The induction tach sounds pretty complicated? I can do a GPS for wot speed however, so I'll do that. I can get the boat to plane with my son up front and calm water sometimes. I'll grab a GPS speed and post back.

Are the hydrofoils bad to use? I hate the idea of drilling into the motor and I wonder how much burden they place on the AV plate? Are they really as good as they say they are?

 

[steelespike]

Re: Yamaha 8hp 2 stroke prop recommendation

The doelfin is pretty effective and seems to have fewer complaints.It probably will steal some top end I would wait and see how the motor does.Raising the motor on the transom may help a little with hole shot and a whisker more top end, depending on how deep the motor is in the first place.We had an I/O and a 50hp outboard with Doelfins The worked well and never seemed to add any strain to the motor.You definitely don't want to be dragging the whole foil through the water with a 8 hp.