Honda 9.9 Power Thrust propeller questions

[HantsCounty]

Hello Iboat People,
I have a new Honda 9.9 long shaft electric start, Power Thrust motor, BF9.9D on a 14' wide body, deep V aluminum boat. I can only get up to around 15km/h at top speed. with just me in it. I understand that the power thrust motor has a 10"x6.5"pitch prop on it so it will gain more thrust, but if I was to switch the prop to my other option 9.1/4" x 8" pitch prop how much more speed will I gain? I use the boat for fishing and that is about it. Will it be worth my money to buy a new prop for the increase in the speed? I dont need to fly down the lake but this is like a light jog down the lake!!! Any help before I waste my money?

Thank you

 

[steelespike]

I couldn't find any info on a BF9.9D do you know the gear ratio?Is it a extra long shaft?
BF9.9 is 2.33 ratio.

 

[HantsCounty]

I couldn't find any info on a BF9.9D do you know the gear ratio?Is it a extra long shaft?
BF9.9 is 2.33 ratio.

its actually a BABJ. Long shaft 20.5" I think the gearing is 2.33:1 on my paper work is says BF9.9 and all the other size motors all have the D too. BF15D etc.
so would changing the size and pitch make much of a difference?

 

[steelespike]

Ok There is a strong possibility the 6.5 was reaching the rev limiter.
​ If you have the 8" put it on as give it a run.Get us the gps speed.
With no tach a 8" is a good starting point. A 9.9 is good for about 20 mph.
A tach would be better but we can get a rough idea with an accurate gps speed.

 

[HantsCounty]

Ok There is a strong possibility the 6.5 was reaching the rev limiter.
​ If you have the 8" put it on as give it a run.Get us the gps speed.
With no tach a 8" is a good starting point. A 9.9 is good for about 20 mph.
A tach would be better but we can get a rough idea with an accurate gps speed.

that would give me 30km/h witch would be a good enough speed for what we need to do. that is twice the speed I am doing now. I do not have a 8" I need to buy one, so should I start with a higher pitch or do the recommended 8" that is stock on the normal units?
they are a bit expensive. I do have a good gps with speed on it. How much is a tach for a boat?

 

[steelespike]

If a 8" is a base prop its a good place to start. and your 14 footer is a size you would expect to find a 9.9 on. For a boat to be called a deep V
the V needs to be about 16-18 degrees at the transom.
A wide body 14 will usually get up better with a load than some of the "smaller" 14s.
There are a number if induction tachs on the market They can be used on a number of motors not exclusive to outboards.
Rule of thumb connect to the bottom plug and get the wire outside the cowl so it doesn't pick up stray pulses.
Sometimes you need to indicate it is going on an outboard.

 

[HantsCounty]

If a 8" is a base prop its a good place to start. and your 14 footer is a size you would expect to find a 9.9 on. For a boat to be called a deep V
the V needs to be about 16-18 degrees at the transom.
A wide body 14 will usually get up better with a load than some of the "smaller" 14s.
There are a number if induction tachs on the market They can be used on a number of motors not exclusive to outboards.
Rule of thumb connect to the bottom plug and get the wire outside the cowl so it doesn't pick up stray pulses.
Sometimes you need to indicate it is going on an outboard.

I will order a 8" and give it a try, we would be happy with even 25km/h
the boat is a 2012 Legend 14' widebody. May not be a deep V but it does require the long shaft 20"
Thank you for the info, I will keep you posted about the differences in speed.