HP prop on 8hp Nissan less power

Plandeck

Petty Officer 2nd Class
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Jul 8, 2012
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I took some advice end of last season and replaced the 3 blade prop on my 2008 8hp Nissan outboard (converted to a thru hull sail drive on my 26' Grampian sailboat you may remember from other posts) with a 4 blade high performance prop....last week after bringing the boat down the river through the lock and out into a ferocious wind on the lake I can report that although there may be more control at slow speeds (reverse responds particularly well) there is a definite decrease in power at high revs as I experience coming across the outer harbor against 50mph winds and 6 foot waves...not sure I made the right decision despite the added control at low harbor speeds.
 

ondarvr

Supreme Mariner
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Apr 6, 2005
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11,527
The power is the same, you have 8 of those little horses. How it gets transmitted to the water may be different though.

​I looked for your old thread about it, but couldn't find it, error messages popped up.

​Do you mean less power or less speed, going to a 4 blade with more blade surface area will give you more bite, going down in pitch may slow you down a bit, a higher pitch may slow you down and feel less powerful, the correct pitch should balance things out, but it's all a compromise, with more of this you get a little less of that.
 

Sea Rider

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Without a tach reading comparison between 3 blade prop and 4 blade new one impossible to determine rpm gain/loss. Know some boaters that have literally screwed best pitch selection going blindly per 4 blade props from current 3 blade ones. To each his own theme..

Any 3-4 blade props you choose must rev under powerd OB's preferably at max wot rpm factory stated as currently loaded.

Happy Boating
 

pvanv

Admiral
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Apr 20, 2008
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That boat calls for at least a 9.8, which is easily accomplished by switching carburetors. The HT props are available in two different pitches; 5 and 7. On the 26, the 7 pitch is likely the best pitch, but only a tach will tell for sure. If you are running the 7 and not reaching 6000 RPM at WOT, you are over-propped. What does your tach say? On my 8,000 pound 28, we run a 5 pitch HT prop. The HT props are high THRUST, not PERFORMANCE, and show their stuff at slow speeds and heavy loads, especially in reverse. They are not for high speed situations. 6 foot waves and 50 mph winds on the Great Lakes in an old 26-foot sailboat is a challenge for any setup.
 

Sea Rider

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As Paul recommends would be an excellenbt idea to swap 8 HP carb for the 9.8 carb. Install an induction tach, go full throttle and check max rpm achieved. From there going for a prop maximization is a must. Find that factory OEM delivered props are way over propped while powering heavy applications, will end lugging extremely the OB if full throttle is required on those harsh boating situations as described..

Happy Boating
 

Plandeck

Petty Officer 2nd Class
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Jul 8, 2012
Messages
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same reliability swapping up to a 9.8 carb? I presume since I installed a solenoid choke in place of the factory installed manual one that I need the remote steering model carburetor....what source do you recommend to purchase an induction tach?
 
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pvanv

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The 8 and 9.8 are identical, except for the carburetor. Reliability is identical; just 22-1/2% more HP. Yes, since the manual-choke carb butterfly operates in the reverse direction of the electric-choke version, you want a carb for a Remote motor (as you have now, I presume). Any Hardline Tach dealer can help you in getting the tach. Or, if you like the big, round, analog tach, the Tohatsu tach is also available, but it does cost quite a bit more than the cheap inductive tachometers.
 

Sea Rider

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Check Hardline model : [FONT=&quot]HR-8061-2 or Tiny Tach induction hour/tachs at Iboats, Amazon. Are cheap and works very nice along prop pitches, a must have installed.

Happy Boating
[/FONT]
 

Plandeck

Petty Officer 2nd Class
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Jul 8, 2012
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you two are quite the dynamic duo...thanks for all the input...can't find the Tohatsu tach...is there a part number?
 

Sea Rider

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As Batman & Robin LOL!!

Tach is unique : 3B7-72530-1 Paul should confirm is code is right or has been superseded.. If having a dashboard will look nice there.

Happy Boating
 

pvanv

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Tachometer with oil warning light (BLACK face). 4 inch diameter
Manufactured by Faria Instruments exclusively for Tohatsu. Gauge has a chrome bezel and is back-lit for easy viewing at night/dusk. Features a domed lens to minimize glare in direct sunlight and a fog & scratch resistant coating.
Part #: 3AC726400M List Price (MSRP): $105.00


Tachometer with oil warning light (WHITE face). 4 inch diameter
Part #: 3AD726400M List Price (MSRP): $105.00

Available from any dealer.
 
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Plandeck

Petty Officer 2nd Class
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Jul 8, 2012
Messages
115
.attached is wiring diagram for my Nissan...don't see any opening for tach leads...
 

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