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Hey guys, I recently bought a 17ft springbok paired with a 40hp evinrude. I am aware that the motors shaft is 20 inches and the transom is 15. I am planning on building up the transom 5 inches. Although I do not want to invest money and time into it if this is not the root of the problem. Attatched is a link to the motor running at full throttle. Any help or suggestions would be very much appreciated! 

 

Link : 

Edited by nickkotowych
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Well that is definatly differant LOL!! Before you go building up the transome you want the prop below the boat otherwise you will experience cavitation, no water for the prop to dig in. It's seems like the water is hitting the motor and it's directed up the shaft, is the motor locked in place, not like there's a lot of space between the transome and the motor?? Maybe tilted back? I'm shooting in the dark right now. A better pic. Would be from the side of the transome, out of the water.

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You answered your own question with the 15" transom & a long shaft (20") engine ;) The water that would normaly be coming off the bottom of the boat and under the engine cavitation plate is hitting the exhaust extension above the top of the plate and being directed up over the transom.

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Well that is definatly differant LOL!! Before you go building up the transome you want the prop below the boat otherwise you will experience cavitation, no water for the prop to dig in. It's seems like the water is hitting the motor and it's directed up the shaft, is the motor locked in place, not like there's a lot of space between the transome and the motor?? Maybe tilted back? I'm shooting in the dark right now. A better pic. Would be from the side of the transome, out of the water.

don't build it to high, just so the cavitation plate is below the transome. Thanks Hank !! Edited by pap
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  You can look at- jack plates boats- on Ebay to get a idea of what you need. Or remove the wood and cap on your transom and put a new piece in. Probably flush with the sides of the boat,have to measure off the distance from bottom of boat to top of transom. Might even have to make it higher. I would not bolt another piece of wood onto the existing wood ,there is to much forward force to hope that it holds up to that constant pounding. In most cases on a aluminum boat two pieces of 3/4 exterior grade plywood will do the trick. Cut them out to size and glue them together. You can then resin the wood or prime and paint it before installing it. Will last forever and maybe 10-20 years painted if the edges are sealed properly. Do not use pressure treated wood on a tin boat.

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I would measure this Johnson shaft. The older Johnsons had a 23 inch long and an 18 inch short shaft. If yours is 23 inch long and on a 15 inch transom you are not only filling up the back of your boat with water, but the length of the shaft also creates a lot of unwanted resistance that lowers the performance of your boat.

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I would measure this Johnson shaft. The older Johnsons had a 23 inch long and an 18 inch short shaft. If yours is 23 inch long and on a 15 inch transom you are not only filling up the back of your boat with water, but the length of the shaft also creates a lot of unwanted resistance that lowers the performance of your boat.

Along with filling the transom , you are raising the bow and losing steering control of the craft .

My boat would take off like an airplane and I had worries about control .

It was dangerous

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Along with filling the transom , you are raising the bow and losing steering control of the craft .

My boat would take off like an airplane and I had worries about control .

It was dangerous

And if it is trimmed to far down it will stick the bow way too far down into the water

Edited by rolmops
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They sell a jack plate that will allow you to raise that motor the 5 "s you need. It will set the motor back some, so you need to be sure your steering, throttle and shift cables are long enough. Here's a link. For a little over $100 bucks it's your simplest solution and you don't need to screw with the boat or motor. Everything stays stock.

http://www.wholesalemarine.com/t-h-marine-hi-jacker-fixed-jack-plate-jp-4fa-dp.html?gclid=Cj0KEQjwpZO_BRDym6K_nMye7cEBEiQAVA7RaKt7lEhbC8lm0o9MhII54JdhXvtXRPF0qMjx-vOeez0aAqmX8P8HAQ

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