Boat Speed - Faster in Choppy water

[DeltaDude]

So, I am using an Alumacraft 145 escape, 25hp motor, I have had this issue for some time just wondering if any of you have any suggestions.

I go over twice the speed when the water is choppy, when it is calm I am going roughly 8-9mph. Choppy I am going roughly 20-23mph.

Any ideas on what it could be and what I could do to fix it?

 

[SuperDaveMT]

In calm water does the boat feel like it's getting up on plane or just plowing water? A friend of mine's duckworth was underpowered and would plow water on the river, but get up on plane in the ocean riding the swells. You may be front heavy, need to adjust your motor trim, or are underpowered (seems like the 25 should be enough motor). You unhooked it from the trailer, right?tooexcited

 

[DeltaDude]

Well, it feels like it is plowing through water, basically the front is up in the air and it goes slow. When its choppy though, the front stays down and we are able to cruise. Moving weight to the front can increase the speed maybe 1-2mph. So max is 8-10mph on calm water, 20-23 on rough.

This is the boat I am using with the 4stroke 25hp yamaha http://nwboatcenter.wpengine.netdna-cdn.com/wp-content/uploads/2014/12/escape-145.jpg

I hope it is unhooked from the trailer


I am taking it in to the shop tomorrow and having a hydrofoil put on, maybe have them lower the motor a bit would help too?

 

[SuperDaveMT]

Make sure it can trim far enough forward(down) to bring the front end down as well.

 

[DeltaDude]

Make sure it can trim far enough forward(down) to bring the front end down as well.

It is an electric trim, I lower it completely with no other results. I dont think the trim can be adjusted any further.

 

[SuperD]

If you are getting those kind of speeds in rough water, it seems like a user error. Some boats come with a block at the trim pistons to protect the motor during travel. If it isn't removed, the trim cannot be fully lowered. Just a possibility. It doesn't seem like a motor performance issue.

 

[DeltaDude]

There is a little lock that you push in when you have the trim lifted up which as you said keeps it from rocking during travel. It is removed before we even back it in the water. If it isn't removed the motor doesnt even touch the water since it can't go low enough.

The guys at the boat shop have suggested the hydrofoil and lowering of the motor itself. Won't test it till next week though, not brave enough to go out on labor day weekend.101ok101


In calm water, the front is up and it feels like we're just plowing through water. Rough water we're pretty flat and feel like we're gliding on top of the water at full speed.

 

[SuperDaveMT]

So any resolution to the speed/planning issue?

 

[DeltaDude]

Hi Dave, thanks for the follow up!

Yes, it did seem to get up to plane rather than plowing through the water.

Max speed was 8mph"ish" it is now 13. 'when it is calm'

Max speed I reached was roughly 23mph



Still considering lowering the engine down a notch, however they said it would affect the RPM.

 

[SuperD]

Lowering slows the boat down, more drag. Performance boats have the cavitation plate right at the top of the waterline. I moved my engine up and got approx. 4 - 5 mph increase. It handles better too. It is a fine line though as high speed erratic turns can cause some cavitation. A better prop could probably help me with that.

 

[DeltaDude]

Lowering slows the boat down, more drag. Performance boats have the cavitation plate right at the top of the waterline. I moved my engine up and got approx. 4 - 5 mph increase. It handles better too. It is a fine line though as high speed erratic turns can cause some cavitation. A better prop could probably help me with that.

I had the default prop to begin with, it was switched out with a speed prop or something like that.

 

[SuperD]

When you are on plane next time, look to see where your cavitation plate is. If your shaft is buried under water, you are too deep and it is actually working as an anchor.

 

[DeltaDude]

When on plane it is out of the water, so much so like you mentioned when you make a sharp turn it loses contact with the water.

When I lower the motor all the way, it goes the fastest, the motor very slightly leans inward, which again lets us get up to plane and go faster. So the motor being | straight up and down isn't as effective as having it slightly tilted toward the boat itself. It is kind of hard to explain but maybe I should grab some pictures or video.

 

[SuperD]

Hole shot is best achieved with the motor vertical. As you get on plane, start trimming it out and you will start going faster. If the boat starts porpousing, you've trimmed a little too much.

 

[DeltaDude]

When I start to trim it up it slows down and the nose pops up causing us to fall off plane.

I can't really trim up at all without it starting to do this.


By the way thank you for taking the time.

 

[gulfstream]

Check under the floor to see if this boat is full of water...just a thought...

 

[DeltaDude]

Its not

Also have a bilge pump.

 

[platypus]

--What happens to your rpm at full trim down vs trim up?
--Seems like you are playing with trim and motor depth and not getting anywhere... so maybe prop size or pitch need to be changed.

--On my boat I have used props 18, 19&20 pitch... same diameter.
--The boat pops out of the water with the 18 but soon over revs... I would use this prop if I had a lot of weight in the boat.
--The 19 makes the boat porpus thus cannot get full throttle when trim up but full trim down I lose a few mph before finding sweet spot.
--The 20 gives me a few mph more than the 19 before it begins to porpus. It takes a bit longer to plane. I settled on the 20 in stainless as the larger lakes I fish the extra few mph at lower rpm and a few extra mph at full trim... smoother ride in the chop for long distance travel is worth it.

--The 19 was probably the best all around prop and I could live with it but could not get it in a stainless same manufacturer. Each manufacturer has some differences in the cup, pitch and diameter of the prop so a 19 in one may not perform the same as a 19 by another.
--Also difference in stainless vs aluminium same manufacturer.

--Some call props with pitch over 20 or near 23 pitch speed props ( on larger motors) I don't know what the speed prop pitch is on a 25 hp. When you get to much pitch and not enough power the boat will plow and not get on plane. Trim will only help if you can get enough initial speed up to get it on plane then trim it up for more speed.
--You will need a tachometer to check what is happening with your rpm at different trims and ensure you don't over rev.
--Changing pitch is like changing gears to hit the rpm sweet spot.... using a speed prop is like trying to take off in high gear... if there is to much resistance you will never get up to full speed. With high hp engine you can start off in a higher gear and get away with it .

--All that being said I think if you most often use the boat at full load you are going to want to go to a motor with the max HP rating for your boat. Prop and trim are ment to fine tune for optimum performance but they cannot fix lack of HP.