top speed for a 1973 Evinrude 6hp on a Sears 12ft semi V

Picked up a 1973 Evinrude Fisherman 6hp for my 1982 Sears gamefisher aluminum semi V boat. Motor has an aluminum 8x7 prop, 8 pitch -7" diameter (factory prop)
had it out yesterday for the first time, and got around 7-1/2 mph gps top speed, with me (210 lbs) 29 series battery (around 80 lbs) gas tank (around 20 lbs) and tm on front (around 30 lbs)
Only way I got to 7-1/2 mph is to place battery at center of boat. If placed back by transom, there was too much weight at back, and it wouldn't get out of it's own way!!!

Thought I'd get closer to 10mph.???
What do ya think?
maybe a different prop pitch???? (which they really don't have much selection in the 6hp)
Was thinking going with a 3 blade, but only ones out ther for it are the same pitch/diameter, and that would only make it more sluggish in hole shot and top end.


8) Thanks in advance, jeff

8) **************UPDATED WITH MORE INFO, IN POST BELOW************ 8)




8)

Sounds about right for the weight.Don't want to over pitch it & lug the motor,worst thing for a outboard.

I have a old 14 ft Sea King that I redid with ideas from here and I used to have a derated 6HP Johnson on it rated at 5 HP. It would push me and the girlfriend and the 65lb. dog about 8.5 mph. With just me and a 3 gallon gas tank, about 11.5 MPH. I sold the 6 HP Johnson and got a 1998 Nissan 8 HP now and it will push us about 10-12 MPH loaded depending on water conditions and I haven't tried it alone yet. Here in Tucson we are allowed 10 HP or electric on the small lakes. The lakes up north can have real boats on them but you couldn't use them for the last few years because they were all low. I sold my real boat and all I have is this little one now. #-o I added a 13X17" hatch in the bow for more storage.

https://www.tinboats.net/forum/viewtopic.php?f=21&t=15880


















https://www.youtube.com/watch?v=a-GFFwJmVFU 6HP Derated Johnson Arivaca Lake Az.

I agree with above statement, sounds right for the weight

well, since this post I went out and got a NICE 1986 Johnson 6hp.


Had it out this morning.
It'll push this same boat (1973 12 ft semi V sears gamefisher) around 18-18.5 mph, gps, with me, battery (mounted midship) and bow mount trolling motor. That's compare to the 9.5'ish that the 73 6hp did. :|
Amazing! The difference between thwe 1973 6hp & 1986 6hp. Prop has some to do with difference. The 73 has a 2 blade, and not sure if correct pitch, but the 86 has a 3 blade 8.5 X 9, and it screams!!! probably hit around low 5,000's rpm at wot with me, tm, battery. 8)

8)

Both those engines look well cared for. I especially like the nissan. It is probably a late 80's early 90, though. They changed the color scheme some time in the early 90's.

I understand this is an old thread but I'll add to it anyway.

When I was a kid I weighted in at 120 lbs, 12' boat and 7.5 sears air cooled eng. With me alone it would hit 14 mph, with a friend of the same weight he'd have to lean way forward to get up on plane.

So either get more power or shift your weight around better , if you can get up on plane your speed will pick up greatly, but is a pia to keep moving forward to get the boat leveled off.