Hey Guys, this is my first post, hoping someone can give me some pointers.

I've got a speed problem, or lack thereof. This is my first mud motor (25hp Kohler, local motor builder frame) - and I knew I would be giving up some speed going to a mud motor, but not this much. I GPS'ed it yesterday with only myself in the boat w/ no gear and only got 11mph... The boat is a 15' Alumacraft that has a 1 foot float deck (so basically a 16' boat). Motor is brand new - has 13 minutes on the hour meter. Max throttle out of the water is 3600 (has a tiny tach) which goes down to around 3000ish in the water. I'm not sure what size prop it has on it - I'll find out. Do you think the prop is causing this thing to be so slow?

Everything I've read from people who have similar setups is that this size boat/mudmotor combo should be getting up close to 20mph without a load.

Any help would be much appreciated.

take that brace off of the skeg, theres no way youre getting your prop far enough in the water with it hooked up like that.

lol I know bud, it was a joke. man i dunno, i had a 25 hp lt and it did 22mph with just me. i would make sure you have a 9x6 or a 9x7 prop. i think your rpms should be higher than that also.

Well if it is the prop its more than likely to big if you can only get 3000 rpms outta it. Your motor doesn't have the power to turn it. If it was too small you would see a high rpm and no power. On a my big blade I can always tell when my prop is wearing down cause I'll gain rpms but loose mph..

There are a bunch of things that can be your problem.

Agree that your RPM's seem to be a problem.. You are hitting the governor OOW but you aren't bumping it at all when running in the water so that is not your problem. When you get it figured out and are bumping in the water, then you can bump it up a little to give you a little more head room, but right now, it is not effecting performance.

There are a number of threads from the past about "tuning" your longtail. Not tuning the motor but tuning the cav plate, adjusting motor so it rides in the water properly, etc... Do a search and see what you can learn.

Also weight distribution is HUGE on these things. Moving people/things around in the boat to see what works best. Moving items (like gas, battery, etc...) to front. Centering things is also important. Boat leaning to one side or other creates a lot of drag and can really slow you down. Sometimes you just have to try different things and see how they are working. ALWAYS use your GPS to determine results. "Feeling" like it is faster or slower is not a good gauge. Also pay attention to making sure you are testing under same conditions-currents, into wind, with wind, etc.

Weight distribution is much more critical than with an outboard and one of the things that is hardest to get used to when making the move. It takes time to figure it out. Moving an ice chest from just off center to centered has bumped the speed up 1-2 mph before. Moving a spare gas can and the other person around picked up about 4-5 mph one time for me....

Not sure how the "hunt deck" or float deck as you called it is effecting you. It changes the angle that the motor is hitting the water and that has to effect you-my guess is it hurts by creating a bad angle on the prop in the water and creates drag, but not sure on that one. I can tell you it will certainly effect the way the boat planes.... And that is why you have to move the weight around to see where it needs to be...

As stated-ck your prop and make sure you have right one.

My guess it is no one thing but a combination of things that you can address that will get you running the most efficient. I would work on my motor and prop first, then start playing with weight distribution.

Do things and then post up results and then folks can give you feedback on other things to try....

Good luck-you will get it figured out....

To big a prop!! The boat how heavy is it looks pretty hefty!!

Thanks for all the suggestions!! I'll post back as soon as I find out for sure what the prop is. Then it sounds like I need to get rid of some weight. This was a project boat for me - and I kinda went crazy adding stuff to it, it's like a neverending project haha. So maybe I added to much crap now it's a big water plow. Here is a before and after just for reference.

Two batteries and a gas tank in back is a lot of weight back there..

Work on getting your motor and prop right, then start moving stuff around...

Are you plowing the water? that would be my guess.... Need to get the boat up on plane...

I agree try moving the gas tank and battery to the front.. and more to the side your not sitting or standing on to try and level out the weight.

In addition to all of the suggestions previously made I would also look at where you are standing. Try to get as far forward as possible and still run the motor safely. Stand in the center when operating. I would definitely look at moving everything forward. Additionally, what does the bottom of your boat look like? If it looks like a washboard, it is going to be slower. If there are hooks at the transom, it is going to be slower. Is the prop running right under the surface? All of these "issues" will cause the boat to run slow. I have tinkered with all of these suggestions over the past 15 years or so with a longtail, and it seems like all of them are different with each set up.

Once again thanks for all the suggestions! I verified that my prop is a 9x5. Do I need to replace it with something steeper? Is there any way to get up to maximum RPM or close to it?

What do you mean by the bottom of the boat looking like a washboard? Guess I don't know what a washboard looks like.

Does the bottom of the boat have dents in it?

A cross braced boat dents and the craters between the ribs resemble a washboard.

A boat don't have to be as bad as the one in the pic to affect performance

No reasonable way to fix it.

Yes it would be a contributing factor, but minimal. First it isn't that bad, ans second not near as critical on a longtail and trying to get the speeds you are looking for. Before anyone chimes in, YES it does effect it, but not critical piece on the longtail...

I would continue to focus on the other things discussed including weight distribution and prop. You say prop is a 9X5-what kind of shape is it in? As Auto said a 9X6 or 9X7 would probably serve you better.... FYI-you can wear a prop down in a heartbeat in sand if you run any of that (or the previous owner did). Seriously, ONE trip can burn one up in the wrong environment.


The other thing that may be hurting you bad is that huntdeck or floatdeck as you called it. If that was not installed properly (looks like you added it based on pics), then that could be a large part of your problem. If the transition from old to new isn't exactly smooth and flowing, you would be creating a lot of drag right there (you are also subject to future hooks right there). In addition, if the rear of the deck is not tapered up a little, with the way the motor sits on there it will have a hard time planing up (which it seems is your problem-not getting on plane). If it is square back there, then you are forcing the front of the boat down and with the motor forward and not anchored at back will have a hard time getting the nose up so you can get on plane. With a long tail, there is a little more room for error than a surface drive, but your angle of push is still going to be wrong. That is why all pods that are added have an upward taper at the rear of the pod...

Good luck and keep at it. You will figure it out.

Great info, thank you. The motor is brand new, so no previous owner, and the only time it's been in the water was for 5-10 minutes a handful of times (deep lake, no shallows or sand). So I know the prop is in perfect condition, sounds like I may need to try to find a 9x7 somewhere and try that. I am also going to remove one of the batteries and try moving the remaining one to the front.

I'm afraid you're right about the lack of taper on the pod, problem is now how do I fix it? Guess I'm gonna have to keep throwing money at this money pit and get someone to hack off the back edge and weld in some aluminum...?

Before you go hacking see if someone else on here has a better idea on what you should/can do.....

Multiple people have mentioned prop wear negatively affecting performance but in my experience a brand new prop with a thick leading edge to the blades can also drop your speed a little. I usually get better performance on my 27hp longtail once the leading edge wears down a little. I also notice a slight increase in the RPM's as the blade wears a little. I have picked up 1-2 mph as the prop begins to wear. I know it is time to buy a new one and change it out when I then start loosing that increase as the prop wears too far.

If you're only running 3000 rpms in the water with a 9x5, don't go to a 9x7 prop or your rpms will be less. Now Go-Devil does recommend a 9x6 or 9x7 for their 23-25hp motors, but I think you have other issues than prop.



I agree with with caddo on this:

The shafts on these motors change for transom height. Do you have the right length shaft for your transom? Also, now that you have that big pod back there, and your motor is mounted 12" inside the new motor, you are changing the way the water is delivered to the prop. The water is getting there later and the angle of the motor may now be wrong.

Notice that the boats putting huntdecks on the transom are also hanging the motor on the huntdeck. Can you get someone to weld a motor mount on the pod and put the motor back there. If you can't or if the pod is not strong enough, you may have to cut it off the back of the boat.

I think every increase in pitch will effect your motor by 200 rpms. At least that was my experience with a 31 lt. If your gonna run heavy loads, try the 9x6. If you mainly run light, I'd go 9x7