2011 Alumacraft Classic 165

I just purchased a 2011 Alumacraft 165 with a Yamaha 20 4-stroke. I can only get about 7-8 mph (GPS)out of it with 2 guys and some gear and only 8-9 mph by myself. Any ideas as to how I can get it up to 12-13 mph with 2 guys. My last boat was a Fisher 16' with a 9.9 bumped up to 15 hp 2-stoke and I was able to get it to 15 mph, no problem, out of it with the same 2 guys and gear. Could this boat have the wrong prop on it? Or are 4-stokes just that much slower? I tried all four pin setting on the motor angle and nothing.

Look down a few threads, there is a discussion about propeller dilemma it may help you...

I would say prop issue for sure..

I was the guy who told Jerry in the other post to go with a four blade prop. So yes i fully believe the fourth blade makes a big difference. With that said that statemtn isnt a blanket for everyones case.

Did you read all of my posts on that thread? Because alot of that can be useful to you in your sitution.

The major difference for you is that you currently can not plane the boat out with the stock prop. Where as Jerry could plane out but one prop stuggled to plane and hte other prop over reved the motor. So he was looking for a fit inbetween two props. He picked up the MPH because a four blade is more efficient due to surface area.

Props can be thought of as gearing for boats. Sometimes you get more speed out a lower pitch prop, like sometimes riding a ten speed bike you might be able to go faster in a lower gear (because it is easier to pedal, you will pedal more rpm but doing less work. Ever try not down shifting up a hill you may be in a thearritical faster gear but you cant push it to that speed)

Honestly I would make sure you are properly set up with the motor before you start swapping props. Get the motor set up on the boat correctly (it maybe, I dont know because it isnt in front of me).

Once everything is set up correcltly, then make a you need to make a choice on props. IMO somthing does not sound correct with your RPM so high and your slow speed. Again it isnt in front of me. but somthing seems off from what i read.

a rule of thumb is you want the antivent plate on the motor to be the same level, and parrallel with the bottom of your boat. That should be a starting point.

If the antivent plate isnt level, i would unbolt it and shim it up to have it level. It is a propper way to ahve the motor mounted. Parrallel the antivent plate to make sure the direction of thrust is in the most efficient angle.

Be sure to have the weight distributed correctly. I know you said your tank and one battery are in the rear and another battery is in the front, But other gear can really add up. So double check that, even remove the unnessary items for the sake of testing.

That is a good starting point.

A thought i have, have you hit anything with your prop? You may have a spun prop causeing the to free spin at higher loads but acts normal at slow speeds.

In laymens terms it is the flat wide part of the casting that is part of the lower unit. It is right above the prop. It is the placce people attach the "whale tails" hydrofoils on to. Which if you have not done it yet, dont do it, not yet at least.

Can you verify that the tach you have is reading correctly? Maybe check it with another tach, or have a good feeling that 5500 rpm really sounds like 5500 rpm? Because some tachs you can set for two stroke, four stroke, 2cylinder, 3 cylinder, 4 cylinder, 6cylinder... It may be set incorrectly and giving us a fasle direction in which to head on figuring this out.

When you are pwoering the moter up when driving the boat around, does the motor noise at some point go from like a motor pushing a load to a like the load has been removed and revs up alot faster? I am asking this to see if maybe the prop has spun like i said before, or maybe you are getting alot of venting in the prop.

H3 that would be great. It sounds like if you have the 9" pitch and are only getting 5100 RPM then it sounds like an 8" may be better. Please let me know how you make out. Do you have the Alumacraft Classic 165? It runs more like a plow than a boat lol. Thanks to both of you guys.

Ok that isnt to bad.

Set the trim to have the antivent plate parrallel to the bottom of the boat.

That should be the most efficient setting for the motor.

When you are out, play around with how the boat is loaded. I know when i am trolling my boat i can pick up or lose .5 mph just for where a person sits.

also try to hear if the motor really sounds like it is spinning over 5k. and how it revs up when you slowly add throttle. You would be looking for it to gain alot of high end rpm real fast. That would be big if infact it has a spun prop or vent really bad.

H3 how did you make out today with your mph test?

Andrew

Thats what I was afraid of. H3 has the exact same boat as I do so waiting to hear back how he did with a 4-blade.

@ 9mph I doubt he was on plane, but I bet he was very close.  All the 16' deep v's I've ever owned (Lund, Starcraft, and Crestliner...all heavy boats) have got up on plane between 9 and 10.5 mph.  And like Anzomcik said...if you do get on plane you'll probably do mid to upper teens. 

jmat,

Wanted to give you an update on my new prop performance. It has been a real learning experience on how weight sensitive our boats are with marginal powered outboards. Lake conditions are also a big factor. Things that did not matter much when I had a 40 hp.

If you recall, on my original thread, I was getting 18-19 mph gps speed with three people (total weight 400 lbs), three gallons of gas and a starting battery.

Last weekend with my trolling battery installed, gas tank topped off(6 gal), and all fishing gear I was getting 15-16 mph up at Presque Isle. I think the trolling battery in the bow was the main culprit since my bow seemed lower while on plane.

This week at Pymy, with 10-12 gal in my livewell, I was doing approx 13 mph when motoring into the wind on a choppy lake. Boat could not achieve plane.

As some have mentioned here and on my thread, I have found the secret to speed is getting on plane. Once on plane the speed increases rapidly. If the weight of the boat or lake conditions inhibit planing, the gain from different props may be minimal.

Now for the really bad news! Last night on pymy my boat ran into one of the infamous shallow sandbars and I trashed the new prop. I ordered another this morning.

Jerry

Jerry,

Ouch did it do any other damage other than the prop? I know I fish up in the stump fields and it does get dangerous up there. I think the problem with H3 and my boats are they are heavy and tough to get on plane with a 20 hp. I think we are stuck with sub 10 mph performance. What really drives me insane is when some of those guys are up there with the big motors they occasionally crank them up. Sometimes I wish they get caught. I only saw it two or three times over the past five years but they sould be required to pull their prop before they put it on the water. I also wish they would incrase the the hp at pymy to 30 or 40. However I don't know if we will ever see that.