Changing from a 9.9 to 18 HP motor

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seadreamers2

.
Nov 15, 2024
3
Hunter 26.5 Pueblo Reservoir
Hi everyone,

The 9.9 hp that came with the Hunter 26.5 doesn't work, and we can't seem to find a used 9.9 with a long shaft, but did find a 18 HP nissan. Does anyone know of any issues we should be concerned about in making this change? It will add about 10 pounds. Thanks
 
D

dlochner

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Jan 11, 2014
12,209
Sabre 362 113 Fair Haven, NY
10 pounds cantilevered out over the transom is a lot of weight to drag around. The 18 hp will also have more torque which could stress the mount and weaken it. Is this a 2 stroke or 4 stroke.

Can you find an 8 hp long shaft? I think that would be a better choice, same weight, slightly less power which in most cases will not be really noticeable.
 
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jssailem

jssailem

SBO Weather and Forecasting Forum Jim & John
Oct 22, 2014
22,116
CAL 35 Cruiser #21 moored EVERETT WA
The 9.9hp outboard was the original equipment on that boat. Adding 10 pounds to the stern will change how the boat sits in the water. If you want to see how the boat will handle the extra weight, grab a 10lb dumbell and suspend it off the stern.

The strength of your motor mount is unknown. Check the mount and how it is attached to the boat to determine whether it can support this extra weight.
 
Captain Larry-DH

Captain Larry-DH

.
Jun 14, 2010
2,208
Robertson & Caine 2017 Leopard 40 CT
dlochner said:
The 18 hp will also have more torque which could stress the mount and weaken it.
Click to expand
:plus: plus you won't be able to use the extra power because your boat won't plane. Even 6HP should be enough to bring it to hull speed, but might be lacking in a strong headwind. An 8 should be more than enough. Look for one that has a sailboat prop (lower pitch and bigger diameter) or if you can find one from the same mfr as your 9.9 you might be able move your current prop over (it should fit but you will probably be "overpropped" meaning your new 8HP will not be able to reach max designed RPM. Emphasis on "might' and "probably") .
 
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L

LloydB

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Jan 15, 2006
894
Macgregor 22 Silverton
My two cycle motor got stolen off my boat and when I went to replace it the dealer reminded me that there are many lakes near me that do not allow two cycle engines to be used on them. So I decided on a fully loaded 9hp four cycle motor with all the bells and whistles including electric start and lift. I had to add a heavy duty Garelick 4-Stroke Auxiliary Outboard Bracket because the original two stroke one was too weak and mounted too high on the transom. Decision made- I like the electric start/tilt but don't but don't care for the extra weight that I have to trailer. If I needed to make the same decision today I think I'd probably go with a backup electric trolling motor and batteries enough to run it 10 miles since my time to destination is based on a date on the calendar. After all it is a sailboat.
 
Joe

Joe

.
Jun 1, 2004
8,119
Catalina 27 Mission Bay, San Diego
seadreamers2 said:
Hi everyone,

The 9.9 hp that came with the Hunter 26.5 doesn't work, and we can't seem to find a used 9.9 with a long shaft, but did find a 18 HP nissan. Does anyone know of any issues we should be concerned about in making this change? It will add about 10 pounds. Thanks
Click to expand
It'll work, but you're basically pouring fuel overboard. Adding a hi thrust prop will help utilize some of the wasted power. Other than the HP you don't say much about the motor... i.e. actual weight, 2 stroke or 4, any amenities such as electric start and remote control. On a lightweight sailboat an extra 10 lbs can change enough that ypu might have to relocate some of your ballast forward.... a least add some chain to the anchor locker. heh, heh. I would also consider looking for a well maintained 8 hp, which is plenty for a 26 footer.... and have less weight hanging off the back.
 
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FastOlson

FastOlson

.
Apr 8, 2010
2,033
Ericson Yachts Olson 34 28400 Portland OR
At 4K disp. that boat never needed more than 8 (or 10) HP in the first place. You'd be surprised/pleased at how well a new(er) four stroke 8 HP engine will push that boat. Spec out the prop for your type of boat, also -- three blade, and not too much pitch.
 
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G

Golden Roo

.
Aug 25, 2018
11
RK 20 20 Trailer Sailer
seadreamers2 said:
Hi everyone,

The 9.9 hp that came with the Hunter 26.5 doesn't work, and we can't seem to find a used 9.9 with a long shaft, but did find a 18 HP nissan. Does anyone know of any issues we should be concerned about in making this change? It will add about 10 pounds. Thanks
Click to expand
just make sure it doesn't hit or grind into the rudder with the prop
 
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C

Crazy Dave Condon

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Jun 8, 2004
10,307
-na -NA Anywhere USA
@seadreamers2

As a former Hunter dealer who sold the and serviced the Hunter 26.5, the transom was designed for a max 10 hp engine following industry standards. Further, you will be plowing at full throttle requiring you to slow down on the throttle. Do not consider an 18 hp; otherwise, you will damage the ob bracket and transom.

Tohatsu use to build the Nissan and Mariner engines. Mercury small engines were also built by Tohatsu but not sure now. The 8 and.9.9 engines.are the same engine but the 9.9 has a larger carburetor. Tohatsu is still in business. A 25 inch long shaft is suggested.

The first recommendation is to take the engine to a moto dealer to see if it can be repaired because it could be a minor thing. Are you using ethanol gas which is not recommended for small gas engines? Forget additives as well as the small carburetors will clog.
Dave
 
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thinwater

thinwater

.
Mar 26, 2011
3,603
Corsair F-24 MK I Deale, MD
I've used nothing but ethanol gas since it came out, 30-odd years ago. Once I learned a few things, no problems since. It works in cars. It's not magic.

  • Keep it dry. Close the vent when not running. No moisture from the air, no problems (cars have sealed systems). Store it somewhere dry int the off season.
  • Use an anti-corrosion additive. I've done the independent lab testing, led the project for ASTM. Most are snake oil (Dave isn't wrong about those) but some are VERY effective. Biobor EB, Stabil 360 Marine (not the red stuff), Texron, Merc Stor-N-Start. The rest are junk.
  • If the motor does not have a filter, add a mower filter in-line. Some small engines have a silly strainer built into the tank suction. It doesn't work.
  • And of course, run the engine as frequently as possible.
Or you could buy ethanol-free gas. But that is impractical in many areas. The nearest place for me is 30 miles in the wrong direction.

Living with Ethanol | Good Old Boat

goodoldboat.com goodoldboat.com
 
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C

captcoho

.
Oct 29, 2012
350
Catalina 30 TRBS MkII Milwaukee
seadreamers2 said:
Hi everyone,

The 9.9 hp that came with the Hunter 26.5 doesn't work, and we can't seem to find a used 9.9 with a long shaft, but did find a 18 HP nissan. Does anyone know of any issues we should be concerned about in making this change? It will add about 10 pounds. Thanks
Click to expand
Seems like a lot of engine just to get out of the mooring area
 
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C

Crazy Dave Condon

.
Jun 8, 2004
10,307
-na -NA Anywhere USA
The major problem with small gas engines are the smaller ports are affected by corn.syrup crap clogging the fine jets.
I tried those so called additives which do not work. Otherwise, I either buy ethanol free regular gas or high test gas that does not contain ethanol.
 
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