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Topic: 12 foot springbok max hp |
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Chrisc54
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i need peoples opinion on max hp on my boat please, its a fairly light boat, i was running a 10 hp on it and it was alright but i would like to go up to a 15 hp short shaft, it would weigh only about 10 pounds more, and its not like i would always have to push it to full throttle, has anyone used a 15 on a 12 footer before or had problems doing so ect.
thanks any help would be awsome
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pajeff
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I am not sure if your question can be answered. Most boats, even smaller ones, have an identification plate that will show max weight and max hp.
I have a heavier 12 ft Hourston that has a 35hp Chrysler, but it is not just the weight, it is the hull type.
I suppose a good question is why you feel the need to have a more powerful motor fitted.
It is also possible that the 10hp is not working properly and not giving full power.
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Fish'n BC
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Your boat should have Canadian and US decals that show the max HP and weight capacity. My 12' Harbercraft is rated in the US for 15 hp and Canada for 12 hp. I'm using a 9.8 4 stroke (and 38 lb thrust minkota) which is already pretty heavy for it. Springbok was bought out and made by Princecraft, so they may be able to give you some advice also, but I noted one of their 12' boats was only rated for 10 hp.
You should also note that if you go to a 15 hp motor, you will be required to register your boat as all boats with a 10 hp or larger motor require (hence the popularity of 9.9s). Alternatively, if you just want it to get up on plane faster: you could add trim tabs to the boat or hydra-fins to the motor. They make a big differance.
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Chrisc54
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thanks for all the great advice guys! no max hp sticker anywhere...also another question do i NEED to have a short shaft on a boat like that or could i go long shaft if i found a good deal...what would happen?
thanks!
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prunehands
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Long shaft is harder on the transom.Obviously you can't run as shallow either
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Edzzed
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I have a 12 ft princecraft ungava that is factory rated to 15hp but I only have a 9.9 2 stroke. To make it into a 15 you only need change the carb, exhaust and prop. All internal dimensions are identical as far as crank, bore and stroke. Put another way, Yamaha makes only the carb, Exhaust and prop as the only differences between the 9.9 and 15hp models. I am pretty sure other makers are the same. After all when dealing with small hp increments you only need change a part or two or three to get the desired effect
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pajeff
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That almost does not make any sense Edzzed. But could it be true.
I think you should just get a good 9.9, too many lakes have a restriction on anything over this size.
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Edzzed
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My gmc diesel runs a whole lot better with a 4 inch exhaust and computer reprogram, That is without even opening up the engine. Look at a car from years ago with a two barrel carb, Put a four barrel carb on it and dual exhaust. Car is gonna have that much more power. An engine is really only an air pump. The better air/fuel can flow, well you get the idea. To verify what I said earlier one only need go to Yamaha's web site and look at the bore and stroke for the 9.9 and 15. If the stroke is different, yes then the crank would also have to be different to take that into account.
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pajeff
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You are quite right, what was I thinking, so you could be out on a lake that is restricted to a 9.9hp outboard and with a tune up kit raise the output to 15hp, say, and fool the regulators into thinking you only have a 9.9hp.
Not sure you could up the exhaust but a bigger carb and polished ports may do the trick.
So think about this Chrisc54, may work for you.
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Hi Speed
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edzzed is correct on his modifications i have done this with a 9.9 merc changed carb and exhaust cost about 300.00 depends on what year your motor is.
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Fish'n BC
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The 15hp motors tend to be bigger with larger cooling systems. You can change your 9.9 for more power, but what about long term side effects? Will it handle the extra stress and heat over the long term or will you end up killing your motor quicker?
I talked to a dealer service mechanic about doing this and he said a resounding NO, the 9.9 and 9.8 are already at the top of their power rating. If this is the case I wouldn't want to sacrifice the life of the motor for short term power gain. Something to consider.
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