Boat Plowing at full throttle

[Led_Junkie]

I FINALLY made it to the river and got underway on my maiden voyage of my 14' Polar Craft Semi-V and 25Hp Evinrude Sportsman ('72). The first shakedown trip revealed an issue that wouldn't allow me to motor faster than 2-3 mph, motor starts and runs great but couldn't throttle up. I found that the spark plug cable was routed in a way that it was binding on the the throttle linkage-Easy fix. Then we got going, up on plane, not real fast, but ok then high revs, and noticable decelleration. This was corrected by dropping the motor to the bottom pin. Quicker acceration, up on plane quick but once past the 3/4 throttle mark the boat begins to plow, throw bow wake, and become unstable. When one eases back on the gas the bow pops back up level and were skipping along nicely.

This was all with myself (220) 11 yo son, cooler, battery, trolling motor, 25lb worth of anchors and 6 rods and a tackle box. I had the gas can and battery with me in the stern, son was sitting center in the forward seat.

I initally thought the prop was spun since I could grab it and twist it about 1/4 inch in either direction (the cavitation issue). <Shrug> When I mounted the motor I placed a level along the bottom of the hull and tried to line up the caviation plate and the hull but ran out of transom. Could I have mounted the motor too high? I have been thinking of making a jack-plate from Aluminum angle as some have done but really have to wait to get funds.

I really need navigation lights first since it is at least running good up to 3/4 throttle. Any ideas would be welcome.

Thanks!

 

[FerrisBueller]

Sounds almost to me that since you put the motor all the way down to the first pin position that once you get up and going, at a certain point the motor actually is starting to push the boat downwards too much causing the "plowing". Maybe try moving your motor to the second pin position?

 

[PGRChaplain]

Move some weight forward and move the motor back a couple holes. Picture the motor angle to boat when the boat is on Plane. Sounds like the motor is pushing the Bow down as stated above.

 

[cva34]

Thats what I would do..All the way down will get on plane fast then start to plow.Get her loaded about even then try dif... hole tell it does what you want.

 

[Led_Junkie]

Are you talking about the trim slots? Where the spring loaded rod gets threaded through the holes and the motor locks onto? If so then I origionally had the motor in the #2 hole position which would hold the motor in a less than vertical position. When I placed it (the rod) into the slot closest to the transom that is when it began to ride better then plow at top speed.

The motor only mounts via screw clamps so I cannot move the motor up and down on a track. I have run out of room on my transom to raise the motor but I have plenty of room to lower it.

I'll have to grab some pics later, if I am mistaken.

 

[FerrisBueller]

Right, there should be different holes where a pin goes through which allows the motor to rest at a certain angle. I think typically people set it to the second pin, but it depends on the loads. The higher up you set the pin the more downward thrust you will have on the rear.

What we were thinking with your is that being its set to the lowest pin position, once your boat planes there is less resistance on the boat and at a certain point the motor is actually pushing the rear upwards causing the front to plow.

 

[Led_Junkie]

Ahh gotcha. I started out in the #2 hole, that is what gave me the "Cavitation" and surging and lack luster performance. Once I placed the motor in the lowest postion the boat ran great until the plowing started.

Could this be from having the motor mounted too low?

 

[Led_Junkie]

I see now...
So now I have to see why I am cavitating then...
Should a prop have any movement when turned by hand?

 

[marshman]

something definitely sounds out of whack... can you take some pics and post them?? i have never had a boat that i had to run set on the bottom pin...youll never get any decent performance trimmed all the way down...

either you have a weight balance issue, or transom isnt straight, or bad prop, or something...im gonna read back through your stuff...

you say cavitated on the second pin?? like prop blowout??( was going on plane, then revved up high but slowed down)

if you blew out, you may be too high(the motor setting that is!! :LOL2: :LOL2: )

second pin should not make you blow out... but the other end of the trim could make you blow out...

i think we need more info...

 

[marshman]

if motor is too low, cavitation wont be the problem....it (the motor)will just plow water and be slow...

 

[Led_Junkie]

I'll grab some pics when I get home.

When I state that I was caviating it felt like it was surging, not the motor but the lower end/prop. I would hear a whooshing sound then the pitch would deepen and I could feel the power climb back up then whoosh/ vroom, whoosh...maybe I am high :LOL2: lol

When the motor was set in the first hole I got no noise and power was smooth until the plow @ 3/4. Before I reset the pin I grabbed the prop and gave it a twist back and forth and there was a measured movement back and forth about 1/4" or so.

I know nothing about outboards so this is all new to me but fun too I like know how things work. Thanks for the help so far!

 

[tomme boy]

Lower it on the transom all the way down and put the pin in the 2nd hole and just run it. You are way overthinking this.

 

[Led_Junkie]

This is my problem I am sure. My transom plate is too short so it is causing the tilting of my motor. Back into the garage to recut and remount <sigh> and I used 5200 to seal the bolts up.

 

[acwd]

Looks like the motor is too high the motor mounting clamp should be touching the top if the transom.

Steve

 

[marshman]

acwd » 29 Jul 2013, 21:25[/url]"]Looks like the motor is too high the motor mounting clamp should be touching the top if the transom.

Steve

maybe...maybe an omc dont like to run high...mercs do...

what does the transom measure bottom to top/top to bottom...?? that may be the blowout issue..

when i first was commenting i think i had your rig mixed up with another on here..i thought for some reason i was talking to the guy with the long shaft motor on the transom riser.....

 

[tomme boy]

The wood you have on the rear outside of the transom. OK it needs to go all the way to the top. That will tilt the motor back in a little. Now, Lower the motor all the way down onto the transom. Put the pin in the first hole. If it still starts to plow, check to see if the bottom of the hull has a hook. That might be why it it plowing and cavitating.

 

[Led_Junkie]

acwd » 29 Jul 2013, 21:25[/url]"]Looks like the motor is too high the motor mounting clamp should be touching the top if the transom.

Steve

This is another concern of mine. With the motor mounted this high the cavitation plate is still below the hull. I guess I will have to fabricate a jack plate. I'm going to stop by Fastenal on the way home from work and price a few pieces of Aluminum angle. thanks for the help so far thanks.

In the short term I'll keep the trottle down. It still scoots across the water nicely but I know it can do much better from reading other posts on boats my size with the same motor getting mid to high 20's

I'll keep updating things as I go. Thanks!

 

[tomme boy]

It does not matter if the anti-cavitation plate is below the bottom of the boat. Lower it on the transom and replace the wood so it goes all the way to the top of the transom and try the different holes for the trim height. You are getting the cavitation from the motor being too high. This is not a bass boat and you do not have a prop made with a cup. If you are getting cavitation, you are also losing water to your water pump.

Don't try to overthink this and save yourself some money. Post a picture with a straightedge down the length of the bottom of the hull at the rear. This will show if the bottom has a hook in it.

 

[Led_Junkie]

Ok I added a temp piece of wood to the plate in the rear of the transom, and dropped the motor all the way down and set the motor in the 2nd hole position. I has thought you had said second but now read that you wanted it in the 1st position.

Performance was this: With same load the boat was much slower to get on plane, but then began to behave same as previously past 3/4 throttle and plowed. I had my son reposition himself in the middle, but the bow rode so high when taking off it was a bit unsettling. Once we planed out it was smooth and the plowing occured at the same speed, granted not as severe. He moved to the forward seat and the high bow problem was solved a bit but the plowing had increased as one would assume.

I didn't get to check the hull for a hook, but I'll try to get that done this evening.

I snap some pics too. Buzy weekend. So my applogies for not posting sooner.

 

[5boats-later]

Hey guys I'm new to tinboats! My boat sat on a trailer with rollers for three years and then I bought it from my uncle. He said that it would flat out haul butt. It's a 15' foot Sears with a 25 hp gamefisher! Yeah I know 25hp gamefisher but I think it was the only made for one year. Any way the boat has a hook in it from the rollers and will now hit WOT because of it. My question is what if I took the boat and rolled it over put pressure on top ( which would be the bottom) and use a 2x6 on top of a car jack and slowly put pressure on hook from inside of boat would that actually work on popping it out!