help with new boat setup

[chris3298]

zul8tr,

Today made a run, with the motor all the way down on the transom and trimmed up to just before level on the cavitation plate according to my marks i made on the motor I was able to top out on GPS at 39.1 mph. I tried many many times to go faster and this is all it would do, which really doesn't seem to bad with a stock crappy aluminum prop.

Motor trimmed all the way down it ran 34.3 mph really is a big difference once you get it trimmed up.

I tried trimming the motor up to where i had made a mark on the motor to give me an idea of the cavitation plate was level. i couldn't quite go that high well I could but was experiencing some porpoising and I was able to ride WOT like that it wasn't out of control or anything.

Where I did have the motor at just before I was level at my mark I must say that the cavitation plate was dam close to running level according to my marks.

Do you think I should try bending the trim tabs a hair more down or just go up one hole with the motor? I'm tempted to bend them a spec more and try it out to get that motor running a spec more level. I was really close to though to my marks.

Hell my marks could even be off a spec because what I thought was level in my garage just didn't seem like that bow road that high in the water.

What are your thoughts?

Wanted to add this motor suposily can run at 5150-5850 max rpm according to the website on the motor/

Thanks
Chris

[JohnsonM50]

zul8tr,

Today made a run, with the motor all the way down on the transom and trimmed up to just before level on the cavitation plate according to my marks i made on the motor I was able to top out on GPS at 39.1 mph. I tried many many times to go faster and this is all it would do, which really doesn't seem to bad with a stock crappy aluminum prop.

Motor trimmed all the way down it ran 34.3 mph really is a big difference once you get it trimmed up.

I tried trimming the motor up to where i had made a mark on the motor to give me an idea of the cavitation plate was level. i couldn't quite go that high well I could but was experiencing some porpoising and I was able to ride WOT like that it wasn't out of control or anything.

Where I did have the motor at just before I was level at my mark I must say that the cavitation plate was dam close to running level according to my marks.

Do you think I should try bending the trim tabs a hair more down or just go up one hole with the motor? I'm tempted to bend them a spec more and try it out to get that motor running a spec more level. I was really close to though to my marks.

Hell my marks could even be off a spec because what I thought was level in my garage just didn't seem like that bow road that high in the water.

What are your thoughts?

Wanted to add this motor suposily can run at 5150-5850 max rpm according to the website on the motor/

Thanks
Chris

Reading along Id say your making good progress. I agree about notes, you can have progress in leaps & bounds but once near potential it gets harder to figure & you might even lose some if you don't document: setup, speed, R's & conditions. If you go for a better prop at some point it will be worth getting the most out of it -if ya wanna go fast
My experience with aluminum boats has it that just passed the point where it begins to porpoise at full speed will likely be where your fastest straight line speed is. Not the best for turning tho. Here's a pic of some easy to make trim tabs:

You'll end up running them fixed but can move em any time. Those in particular are mounted 1/4" up from the bottom so act like a step for less drag. At the rear of the tab for that boat they work best at about 1/8" up from the bottom. Good Luck

[chris3298]

Reading along Id say your making good progress. I agree about notes, you can have progress in leaps & bounds but once near potential it gets harder to figure & you might even lose some if you don't document: setup, speed, R's & conditions. If you go for a better prop at some point it will be worth getting the most out of it -if ya wanna go fast
My experience with aluminum boats has it that just passed the point where it begins to porpoise at full speed will likely be where your fastest straight line speed is. Not the best for turning tho. Here's a pic of some easy to make trim tabs:

You'll end up running them fixed but can move em any time. Those in particular are mounted 1/4" up from the bottom so act like a step for less drag. At the rear of the tab for that boat they work best at about 1/8" up from the bottom. Good Luck

Thanks I wasn't sure if anyone else would reply, heck with over 200 views and two people now chiming in I really do appreciate it. This boat is my fishing boat but I do like to go fast.

You're right tonight I will start taking some notes for what I have done so far, I'm not sure if I should raise the engine up one more hole or try and bend the tabs a spec more?
I'm leaning towards raising the motor up one hole on the transom because I feel the tabs are bent pretty close to equally and I'd hate to bend them more and end up screwing up and loosing the progress I already have.

I think I'll go up one hole on the motor because i can easily come back down if i need to.
I may do that tonight and try again tomorrow and see what happens.

Thanks for posting that homemade trim tab I may end up going to that later on. This style trim tab how long is it across?? and should I maybe even make them wider?
I see the plate looks like maybe aluminum, is the hinge stainless??

I will go with another prop down the road but kinda want to experiment and get the most that I can with the setup and it's good learning experience.

I'd like to know could I see 50 or 55mph from this boat and motor setup? I know this motor can't be hopped up because it is fuel injected I'm sure there is more that can be done with the carb version and who knows later on I may want to look for the carb version of this motor or maybe a mercury 40 to play with.

I have to say though this speed stuff is addicting

Thanks
Chris

[JohnsonM50]

Thanks I wasn't sure if anyone else would reply, heck with over 200 views and two people now chiming in I really do appreciate it. This boat is my fishing boat but I do like to go fast.

You're right tonight I will start taking some notes for what I have done so far, I'm not sure if I should raise the engine up one more hole or try and bend the tabs a spec more?
I'm leaning towards raising the motor up one hole on the transom because I feel the tabs are bent pretty close to equally and I'd hate to bend them more and end up screwing up and loosing the progress I already have.

I think I'll go up one hole on the motor because i can easily come back down if i need to.
I may do that tonight and try again tomorrow and see what happens.

Thanks for posting that homemade trim tab I may end up going to that later on. This style trim tab how long is it across?? and should I maybe even make them wider?
I see the plate looks like maybe aluminum, is the hinge stainless??

I will go with another prop down the road but kinda want to experiment and get the most that I can with the setup and it's good learning experience.

I'd like to know could I see 50 or 55mph from this boat and motor setup? I know this motor can't be hopped up because it is fuel injected I'm sure there is more that can be done with the carb version and who knows later on I may want to look for the carb version of this motor or maybe a mercury 40 to play with.

I have to say though this speed stuff is addicting

Thanks
Chris

Replies, Its not an unfriendly thing, more a probable concern for your well being in as much as hopping up a standard boat being dangerous. When it comes to going fast of course the danger meter goes up just as fast or more. That said you are working with a motor within your boats capacity right? So reaching its potential is good experience. Just be careful, wear the vest when you intend to play with the speed, a helmet if it gets really fast. 50 is kind of a milestone for non racing boats, especially those w/o tons-o-hp. To reach it at all would be surprising.
The trim tabs are 1/4 aluminum, The continuous hinge is SS. I threaded & loc-tite-d the hinge to the aluminum & ground the screws flat on the bottom. The turn buckles are from Loews, the mounts are just junk I had around. They are about 5" wide & 4" long. The boat is 11'8" so somewhere in proportion should help. If you over porpoise the boat be prepared to start repairing leaks the pounding takes a rapid toll Good Luck
"The speed stuff", If the bug bites hard enough, consider racing. There you get to go for it knowing that tow boats, water rescue, & EMT's are there for you. At that point the replies to your requests will multiply.
It would seem that you are young, maybe even a minor?, please take no offense to that, just to say that if you are be sure your Dad knows what you're doing

[chris3298]

I was kinda thinking the same thing that people don't want to say because of the danger factor. I always wear a life jacket when in the boat by myself or with others, anyone who rides in my beat wears a life jacket if not they don't ride, not wearing a life vest you're an idiot plain and simple. I wear that safety cord hooked to my life jacket or wrist at all times again you're an idiot if you don't.
I have a friend who won't wear one, I know he can't swim that great, i'm just waiting to get a call someday from his mother saying he's dead but thats his choice. Preaching doesn't do any good about safety with him.

The boat is well rated as a commercial boat, if i ordered it as a recreation boat it would have had a sticker that said max HP would be 40 so I'm 10 over which don't feel that is a lot.

Sorry if I sound young I have had many times people think I'm 10 years younger then what I look, I'm 32. DAD didn't buy this boat and motor only thing he did was give me a trailer for it that is probably older then me which I had to go through and replace every bolt with stainless and buy a new axle. I probably should have bought a trailer for all I had to do to it. So a minor yeah I'd say I'm a minor at heart, all my friend are married and having kids and I'm just looking at what is the next toy i can buy hahaha

There is a place that does racing down here in Louisiana, I think it's in like Alexandria Louisiana which is good drive aways for me, it wouldn't make much sense in getting into it for what I'd have to drive to race.
Bogalusa Louisiana there is a boat club which does some drag racing now this I'd really like to go and participate in there about 20 miles away if that.

Thanks
Chris

[JohnsonM50]

I was kinda thinking the same thing that people don't want to say because of the danger factor. I always wear a life jacket when in the boat by myself or with others, anyone who rides in my beat wears a life jacket if not they don't ride, not wearing a life vest you're an idiot plain and simple. I wear that safety cord hooked to my life jacket or wrist at all times again you're an idiot if you don't.
I have a friend who won't wear one, I know he can't swim that great, i'm just waiting to get a call someday from his mother saying he's dead but thats his choice. Preaching doesn't do any good about safety with him.

The boat is well rated as a commercial boat, if i ordered it as a recreation boat it would have had a sticker that said max HP would be 40 so I'm 10 over which don't feel that is a lot.

Sorry if I sound young I have had many times people think I'm 10 years younger then what I look, I'm 32. DAD didn't buy this boat and motor only thing he did was give me a trailer for it that is probably older then me which I had to go through and replace every bolt with stainless and buy a new axle. I probably should have bought a trailer for all I had to do to it. So a minor yeah I'd say I'm a minor at heart, all my friend are married and having kids and I'm just looking at what is the next toy i can buy hahaha

There is a place that does racing down here in Louisiana, I think it's in like Alexandria Louisiana which is good drive aways for me, it wouldn't make much sense in getting into it for what I'd have to drive to race.
Bogalusa Louisiana there is a boat club which does some drag racing now this I'd really like to go and participate in there about 20 miles away if that.

Thanks
Chris

Cool, Drags would be fun. Im I took my hydro to drags & had a blast. There's no real close racing here either but close enuff, 20 miles aint bad.

[zul8tr]

If you want to hit 50 you are going to need rpm in the 6900 - 7000 rpm area and that is going to be difficult to do on your alum boat with the present engine and prop. Your engine might not take 7000 rpm for extended time??? Your present prop even lifted high would probably still limit the engine rpm but you can try to go higher on the transom before trying different props. I think it will definately take a smaller diameter and greater pitch prop with the engine really lifted high on the transom so that the prop shaft is close to the bottom to get the 7000 rpm area.

So far with the set you have you are close to the speed estimate I made at a prior post for the 5500 rpm range at about 39 mph so keep going and don't forget the notes. You still need a tach for rpm..

[chris3298]

Wow I know this motor won't run that high in rpm I'm sure the rev limiter would kick in. We'll just have to see what happens in the future. I'll keep going and see what happens though but you're right I need to shoot a email to tiny tach and see if that will work on this motor. I'm keeping notes now i have written down what I have done now so far.

Raised the motor up one hole last night gonna go get some gas and try it out again today.

Chris

[zul8tr]

Looking at the photos your engine has the water pickup screen about half way between the prop shaft and the anti-cavitation plate. So you will be limited to how high you can raise the motor before water starving the cooling. As you raise up take note of the cooling water discharge when up on plane. My visual guess is you can raise the motor so the anti-cavitation plate is about 3" above the bottom. You will also know if you are too high because the boat will not plane over and the prop will cavitate. This alone might be the limit with your hull and motor. As you raise the engine the prop will free up and engine rpm will increase and you could run out of prop pitch i.e. not enough pitch. Then a different prop is needed. Testing will reveal all of this

[JohnsonM50]

Ive found a standard prop to fail at traction before the flow was interrupted by height but each rig being different that needs to be watched. Most motors would scorch pretty fast run hard w/o water.