15" shaft versus 20" shaft

[paulpost]

Hi again, I've bought a Saturn 12' and now I'm looking for a 15 HP outboard.
According to all that I've learn, this boats and inflatable boats in general are designed to be equipped with 15" shaft engines. My problem is that I found a brand new 15hp Yamaha that has been stored for 10 years for $1000 but has an 20" shaft. How bad will be to use it on my inflatable?
Thank you

 

[kandil]

Re: 15" shaft versus 20" shaft

Very bad if you have to use this one you well need to install a jackplate or a mini jacker you can get it on ebay for less than a $100 http://cgi.ebay.com/ebaymotors/_Boa...arms=39:1|65:1|240:1318&_trksid=p4506.c0.m245

 

[Sea Rider]

Re: 15" shaft versus 20" shaft

According to all that I've learn, this boats and inflatable boats in general are designed to be equipped with 15" shaft engines. My problem is that I found a brand new 15hp Yamaha that has been stored for 10 years for $1000 but has an 20" shaft. How bad will be to use it on my inflatable?
Thank you

Justa a comment, a friend of mine is using a Yamaha 25 HP long shaft on a Zodiac 3.50 with inflatable floor rated to just 20 HP short shaft. He's been using this configuration for years with no transon & related parts prob at all, he offers surf towing services daily and has to cross 2 meter white water 10waves series in a row to get into the surf towing area. As long as you don't exceed the engine specs on your plate transon will be ok. Anyway if in tech doubt, ask the owner for a test ride and test for yourself the engine/boat performance. Inflate your sib well to recommende working pressure on all tubes. The price is about fine, if engine in good conditions don't let go this opportunity. A 12 Saturn can handle a 20 HP or pehaps a 25 HP well. You can first try the engine with out the extra engine plate mount and then buy one if needed.

Happy Boating

 

[Muzza]

Re: 15" shaft versus 20" shaft

Just a quick note on the 12' Saturn: It is rated to 30 HP. I have that
boat and run a 25 HP Shortshaft. The boat is very quick with just me on it but things change if I add my wife and two kids. It will still plane with everyone aboard but I would like a little more power.I am currently looking for a 30 HP motor. I use the boat in open ocean and have yet to test on flat water where I'm sure it would fly.
Happy Hunting
Muzza

 

[Sea Rider]

Re: 15" shaft versus 20" shaft

Just a quick note on the 12' Saturn: It is rated to 30 HP. I have that
boat and run a 25 HP Shortshaft. The boat is very quick with just me on it but things change if I add my wife and two kids. It will still plane with everyone aboard but I would like a little more power.I am currently looking for a 30 HP motor. I use the boat in open ocean and have yet to test on flat water where I'm sure it would fly.
Happy Hunting
Muzza

Hola Muzza

What brand is your actual 25 HP in use ? 2 or 4 strokes ?

 

[lester]

Re: 15" shaft versus 20" shaft

I have the Saturn SD365 12' inflatable boat as well. I have a late model 15hp yamaha two stroke short shaft on it and it works beautifully. I found that I wanted a little more power to do some wakeboarding with it and acquired an late model Yamaha 25hp two stroke long shaft. I would have to say I do not recommend using the long shaft on this transom without any modification. First off, having the prop down those extra 5" gives you alot more transom torque and made me a little nervous watching the transom bow like that (it wasn't that much, but compared to how rock solid it performs with a short shaft, made me nervous). Also the longer shaft will sit deeper in the water, making the cavitation plate create much more drag which robs you of top speed. Lastly, on the Yamaha 25 long shaft, the shaft isn't thin until under the cavitation plate and this caused alot of water to shoot over the transom into the boat due to so much of the wider portion of the shaft being on the waterline. I would either get a jack plate for your transom or hold out for a short shaft. By the way, the 15 two stoke Yamaha is nice on this boat...I wouldn't go any lower on the HP however. Good luck.

 

[Muzza]

Re: 15" shaft versus 20" shaft

Hi Sea Rider
I have a 1974 Johnson 25. It's a two stroke shortshaft. It's a good motor, but being my
first outboard, I have nothing to compare it to. I'm curious as to how it would
stack up against newer models. What I really want is a 30HP Yamaha (3cyl).
two stroke....tough to find a used one tho'.

Muzza

 

[Sea Rider]

25 or 30 HP ?

25 or 30 HP ?

Hi Sea Rider
I have a 1974 Johnson 25. It's a two stroke shortshaft. It's a good motor, but being my
first outboard, I have nothing to compare it to. I'm curious as to how it would
stack up against newer models. What I really want is a 30HP Yamaha (3cyl).
two stroke....tough to find a used one tho'.

Muzza

Hello Muzza:

A 30 HP is too much for a 12" sib (3.65 mtr), generally rated for max 20 HP, some of my clients are using 30 HP on 380 sibs, too much power, the under side bottom rails from transom alum floor will suffer it's consequences in the long run, unless extra rivets are added to hold better. Stick with a new 25 version if available, 4 strokes engines weights about 10 more kilos compared to same 2 strokes engines. A 30 Hp 3 cylinder, will weight more than a 2 cylinder engine. See pic of what I'm talking about. Keep in mind that new sibs are lighter compared to same old models, made of hypalon and thicker alum floos boards that holded more HP's.

Happy Boating

 

[Muzza]

Re: 15" shaft versus 20" shaft

Hi Searider
Why would Saturn rate their 12 footer for 30 HP if it couldn't handle it?
All I'm saying is that when I have my family on the boat I could use a little more power. I've got an air floor by the way.Maybe we should start a new thread ...seems we've hijacked this one and gone off topic.
Muzza

 

[George Zeck]

Re: 15" shaft versus 20" shaft

Muzza -

I would focus on the weight the Saturn can handle; getting the extender plate can only help you sleep at night.

I looked at the Saturn v. Avon (RIB) -- bought the Avon due to warranty issues of the Saturn (simply, I did not get the warm and fuzzy feeling once I read the small print).

Make the call to Saturn and find what weight it can hendle; big diff in weights between a 30HP 4 stroke vs. 2 stroke.

Good Luck -

George

 

[jamesdeanj]

Re: 15" shaft versus 20" shaft

I have a Yamaha 25 2 stroke on my Futura Mark 2HD. It's 13.5 with aluminum floor. It requires a long shaft because of tube diameter. It moves great with one or two people in it. Up to 27 mph.

You would probably need a transom jack. But I would keep looking.

 

[Sea Rider]

Re: 15" shaft versus 20" shaft

Hi Searider
Why would Saturn rate their 12 footer for 30 HP if it couldn't handle it?
Muzza

If the boat can handle a 30 HP it's ok, don't know Saturn brand specs, so assumed max 20 HP for normal 12" sibs. Put max engine rated on the transom plate.

Happy Boating

 

[tomalt]

Re: 15" shaft versus 20" shaft

From where to where on the outboard do you measure to figure out your shaft length to see if it is a 15" short or 20" long shaft?

Thanks

 

[tashasdaddy]

Re: 15" shaft versus 20" shaft

you measure from where it sits on the transom, to the flat plate just above the prop.

 

[tashasdaddy]

Re: 15" shaft versus 20" shaft

Paul, before you test that motor that has been sitting 10 years, there are some things that need to be done. http://forums.iboats.com/showthread.php?t=158086