Will I be ok?

[greatoutdoors]

Hi Guys. I am in the process of rebuilding my 2 short shaft motors for my 14' Aqualine aluminum semi-v, so in the meantime for the rest of the fishing season, I put my 40 hp Merc on it. The transom on the boat is a tad under 16". The shaft on the 40 hp is about 20". Is this going to cause a problem? If I tilt the motor a little, I can get the cavitation plate to 4" below the transom. Is the prop going to be too low in the water?

 

[hwsiii]

Re: Will I be ok?

Wayyyyyyyyy too low, but theoretically all it will do is slow the boat down, and you will have faster speeds when you finally get the short shaft motor back on it.


H

 

[greatoutdoors]

Re: Will I be ok?

Well, I got the boat out on the water today with the 40 on it, and it flies! 40 horses pushes a little tinny 14 ft'er along quite nicely. There was a pretty strong wind on the lake today, I'm estimating with the wind at my back I was nearly at 45mph. First I had the motor flat against the transom but it was kicking up to much water into the back of the boat, so I tilted it up about 4" and no water in the boat. I was expecting a big rooster tail from the shaft being too long, but it was fine. If I can get a jack plate to lift the motor to where the cavitation plate is about an inch below the bottom of the transom, approximately how much more top speed can I expect?

 

[steelespike]

Re: Will I be ok?

Really hard to say what the increase would be but under ideal conditions with a proper shaft length 2" could get about 2 mph.Odds that a stock 40 on that boat doing actual 45 are slim.Would be interesting to see actual performance.

 

[greatoutdoors]

Re: Will I be ok?

I can't say for sure what the speed is, but it sure feels in the 40-45 range. I don't have a GPS or a speedo on it, but what I tried to do is get as close to shore as I safely could and compare the speed that I'm passing the stationary objects on shore to what they look like in a car. The boat only weighs around 300lbs with the motor and battery, and I'm 195, so that's only495lbs. That's a pretty good power to weight ratio. There's got to be a way to figure it out. It's a 14 ft semi-v aluminum with a 1970 40hp Merc. The motor is like new. 160lbs of compression in both cylinders. I use octane booster in the gas mix. Probably doesn't make a difference, but it never hurt. Anyone have a way to calculate it? I don't want to buy a GPS...

 

[superbenk]

Re: Will I be ok?

Anyone have a way to calculate it? I don't want to buy a GPS...

Time how long it takes to go between two landmarks exactly 1 mile apart. Maybe you could use the ruler tool on Google Earth to find the distance between two points on your body of water. Once you have that time, it's simple math to figure out your approximate speed.

This is definitely not very accurate though. Your pitot speedo is probably more accurate than this method.

 

[steelespike]

Re: Will I be ok?

Find a spot with a nice straight exposure close to shore.In a car drive say a 1/2 mile or a mile and some how mark it off.Maybe just park a car at each end. No need to see the hole thing from the boat just the two markers.The tricky part is to sight straight at the marks perpindicular to the boat.measure the time to go through the marks.
Pretty involved.No friend or relative with gps?A second choice is a friend with a speedo on the boat(not very accurate)
If you had a spot you could run really close to shore without getting arrested
And still be able to measure 2 markers.You might only have to go a couple of hundred feet make several runs and get an average.