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The little Check that could

Here is a picture of the half step blocks I made . They were set in epoxy and screwed fast . They have solid 100 % contact between the blocks and the mounting surface .

http://20hpMerc035_zpse1b55b43.png
 
My hand tied harness worked fine . I used 3 sections of 12' rope .
I would also like to give thanks to my buddy Tyler for his help .
(that's him in the photo)

20hpMerc034_zps7cf8d829.png[/URL"]http://20hpMerc034_zps7cf8d829.png]

http://20hpMerc033_zps64bfbd29.png
 
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The ballast is all the way forward and the motor has been raised 1 3/4" .

With the jack plate at the top , the center line of the propeller is 3/4" below the pad . I will need to watch the working water pick up level .

From the rear of the stern to the front of the propeller is 25 inches . The motor has 6 inches of set back .

I will try to get out for a test run this week after work .
 
Test run results were interesting . Slight chop perfect for speed . As for the ballast , boat planed out decent . Had ten gallons of fuel ( 60 lbs ) . Top speed was 25 mph/gps . I could run the jack plate to the top and maintain water pick up (3/4" below pad) . I could see the top of the hydro foil at the waters' surface , bottom side was running wet . The best setting was around 1 3/4" to 1 1/2" below the pad ; rpms 5600 . It would do 5800 rpms with occasional slips . If run up in height to get 6000 it was slipping . At top height 6200 rpms slipping . With this propeller I notice the motor shook a little harder , I could see solid motor mounts helping out . I'll see about machining a set , be a fun project for the lathe . Turns were acceptable , those cupped blades bite in nicely . Would start to slip if laying the boat over more aggressively .
 
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Steve, when I was just a kid I built a 10' wood boat (90 lbs) and put a 30hp Johnson on the back (110lbs). Motor came with a 10"x11P prop (3 blade).
Shot out of the hole like getting hit by a moving bus, but wasn't fast enough. I purchased Michigan 2 blade 10-1/4" x 17P prop. Was only able to get 4600 rpm. Had the OD of the prop cut down to 10" and gained 200 rpm. As a last resort I had the OD cut to 9-1/2" and got back to 5300 rpm. This still kept the pitch at 17. The boat still accelerated very well but ran much faster. No GPS back then only the ego meter. That registered just at 60 mph. I now doubt that was realistic after doing 60 in a Starflite.

The hull was a flat bottom with .5 degree dead rise.

My cousin had a 13' hull just like the Playmate, only it was a flat bottom design. With a 50 hp Yamaha on the back the best GPS speed was 42mph and very hard to make turns at speed.



You are doing real well with that 20 hp 4 stroke. You can be proud of your accomplisments. Just think of all the fuel you are saving with that small motor and still running in the mid 20's.

If we all set our boats up with the same results as yourself we would be spending less in fuel costs at the same speed.

Good luck!
 
I'm going to put the 11.5" pitch prop on again and test . Although I could already raise the motor high enough to make it slip , this is first run since changing the ballast position .

It is appearing that 25 mph may be the limit . Curious though the 11.5" pitch (6200rpm) and the 13" pitch (5500rpm) topping out at the same speed .

I'm thinking it will take increasing the diameter to get above 25 . Possibly trying a two blade prop in the 13 , 14 , 15 inch pitch range .

I'll try the 10 x 13 prop again also .
 
Here is a pic of the prop from Hill Marine , going to call Ron today with the run information and get his opinion on which way to go in the prop department . Not sure if you can see how the blades are cupped .

http://CheckmatePlaymate87013_zpsd01a58ec.png
 
I snuck down to the lake today , had the 10.1 x 13 prop on . 21 mph/gps at 5600 rpm one inch below the pad . At top height (3/4" below pad) 21mph , 5900 rpm . If I lowered the prop till it grabbed , the speed would increase to 22 mph while the rpms dropped to 4600 .
This prop and the 4 blade are being retired to the wall . At the end of the thread I will post results for all four propellers . I haven't spoken with Ron yet , I wanted to see what the ten inch diameter could do since raising the motor . Next up the 11.5 pitch .
 
Summary

It's been fun and educational tweaking the Playmate with the 20 hp .
However , I miss the raw power of acceleration .
Hence forth my official declaration of joining the dark side of deception :(
I've been crunching the numbers and find 258 lbs left for me and gear after this power plant swap .
Fake stickers . That thinking small . Think BIG , fake outboard !
That's Right ...
This would be the real motor :
MUHHAHAHA !!!!

http://200hpjet_zps77a3526c.jpg

http://www.mercurymarine.com/engines/jets/optimax-sport-jet/
 
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