Wrong pitch or am I doing something wrong?

[Bigpat5123]

I have a '72 sears gamefisher 12' semi-v fiberglass boat. I am powering it with a 1985 mercury 9.8hp with a fresh rebuild that runs mint. The boat weighs about 200lbs or so by itself and the motor is 65lbs. The motor has the standard 9x9 two blade prop on it and I also have a 9x8 three blade that I havent tried yet.

The max hp capacity of the boat is 14hp and person capacity is 575. So I got the biggest motor I could find under the rating so i assumed it should get this boat on plane with two people in it. But while taking the boat out it doesnt seem to be going/planing as well as it should.

So my question would be; is a 400lb load to much for a 9.8 with a 9 pitch prop powering a 12' fiberglass boat? Should I try a 7 pitch prop or any suggestions would be great.

 

[gcboat]

Re: Wrong pitch or am I doing something wrong?

I'm going to say you're just underpowered plain and simple. As far as the other prop is concerned I guess you'll never know til' you install it.
I'm making the assumption that the bottom is clean.

 

[countvlad]

Re: Wrong pitch or am I doing something wrong?

I have a '72 sears gamefisher 12' semi-v fiberglass boat. I am powering it with a 1985 mercury 9.8hp with a fresh rebuild that runs mint. The boat weighs about 200lbs or so by itself and the motor is 65lbs. The motor has the standard 9x9 two blade prop on it and I also have a 9x8 three blade that I havent tried yet.

The max hp capacity of the boat is 14hp and person capacity is 575. So I got the biggest motor I could find under the rating so i assumed it should get this boat on plane with two people in it. But while taking the boat out it doesnt seem to be going/planing as well as it should.

So my question would be; is a 400lb load to much for a 9.8 with a 9 pitch prop powering a 12' fiberglass boat? Should I try a 7 pitch prop or any suggestions would be great.

how many people were on the boat when you were trying to get in on the plane? have you tried to run it with you only?

if you have a 7p sure give it a try see how it does...if you dont theres always a good idea to have a spare prop.... good luck

 

[junior1113]

Re: Wrong pitch or am I doing something wrong?

i have a 78' 9.8 thunder bolt. it does great with 9 pitch 3 blade. 12' landu alluminun jon with 500lbs of people and gear and gas. 18mph. do you have motor up high enough? where is cavitation plate in realation to bottom of boat? can you post a pick of back of boat with motor where you run it at.

 

[Bigpat5123]

Re: Wrong pitch or am I doing something wrong?

Thanks for all the reply's. I can post some pics of my setup tomorrow to show you what Im working with. I believe the AV plate is about an inch to 2 inches below the beam of the boat. I will take a picture to show actual and measure it when I get home.
I do not think I am under powered as a 10hp motor should be able to power a 12' boat with two people no problem. Next time I go out I will take my gps to see the speed.

 

[Bigpat5123]

Re: Wrong pitch or am I doing something wrong?

All,
I noticed that my AV plate was about 1 1/2" below the beam of my boat. So I made a mini jack plate out of wood, as I am a avid woodworker to just try to bring the motor up to see what happens. I took the boat out with two of my buddies the other day and it seemed to be working well but with 150 lbs over the max weight of the boat we were mostly just trolling. I will hopefully try it today by myself to see how it runs. I will let you know.

 

[Bigpat5123]

Re: Wrong pitch or am I doing something wrong?

I took the boat out last night and it performed very well. I put the jack plate and the 9 x 8p prop on it with just myself in the boat. I could hear the difference in the motor once it got out of the hole and into the top of the rpm range and ON PLANE!!!!!!! never got there before yesterday. The make shift jackplate seems to be the ticket as I was having too much drag to get up on plane.
I am making an aluminum jackplate as we speak to permanetly fix to the boat. I did not have my gps with me due to my parents taking it on vacation with them so I couldnt get an actual speed but I will next week when they are back. It was going as fast as I was expecting with the upgrade to the 9.8hp from the 6hp. I would guess the 13-16 mph range.

My observations-
-Windy/choppy day on the 300+ acre lake
-300lbs. of me and motor on or behind the rear bench seat
-3.5 gallon gas tank in front of middle seat
-Due to the weight distribution it took a lil while to get out of the hole and on plane but once it did ran flawlessly.

Next test-
-Take my girlfriend with me and put her on the front bench seat
-Try with the 410lb +/- load and see how it performs with more weight up front to hopefully keep the bow down

I will keep you all informed and thanks for the help. It was amazing how much better the motor sounded just because I raised it up 1 1/2".

Any thoughts/comments/suggestions would be great!

 

[Bigpat5123]

Re: Wrong pitch or am I doing something wrong?

I had a chance this weekend after I got back from vacation to take the boat out by myself agian but with the GPS. I clocked in at 19mph with the same details as the above post under "my observations". I was fairly impressed with my results and the boat would stay on plane down to about 13-14mph. Not bad for a 12' boat.
I will hopefully have a chance to go out today with the girlfriend and see how it does. I will let you know when that happens.

 

[junior1113]

Re: Wrong pitch or am I doing something wrong?

u could go to 7 pitch and foil for better whole shot. tiny tach would tell you exactly which way to go to get maximum life out of the motor.

 

[Bigpat5123]

Re: Wrong pitch or am I doing something wrong?

I took the boat out yesterday evening with my girlfriend finally but forgot the GPS. It seemed that we were probably in the range of 14-15mph on plane which isnt too bad for a heavy boat and 400lb load for a 9.8 in my opinion. What do you think?
The engine sounded good once it got out of the hole and on plane, a nice mellow whine.
Junior1113, I have been thinking about trying a 7 pitch prop but keep debating wether or not I want to lose some top speed. Wont be that big of a jump either way but would be worth a shot. Like you said I may try to get a tach for it and hook it up to see how Im doing for RPM and then maybe switch props. I will let you know how I make out when I take the GPS next time.