EricM boat/motor/jackplate/prop help please

[EricM]

1998 Baymaster 19.5' center console tunnel hull w/modified vee, rated for 150 hp
1996 Honda 90 hp four stroke, seems to run beautifully
No jack plate, motor as low on transom as possible
Aluminum 3-blade 13 1/4 x 16 prop

My new (to me) set-up is giving me some problems and I'd like some help please. Alone or with another passenger - plus everything I own (lots and lots) stowed in it - the rig gets on plane and runs at a speed of about 24 mph and max rpm of 5300-5400 when trimmed. Any more trim results in the beginning of porpoising. Empty with me only (no gear) it gets 28-29 mph and too much trim makes it cavitate. I would have thought it would have run 35 or so anyway??

The problem arises when I put 4 of us in the boat, and maybe some water in the bait tank. The rig won't get on plane - or does it extremely (extremely!!) slowly, depending on where everyone is seated. Trimming helps, but overtrim causes cavitation. Does anyone have any particular ideas? I know it is underpowered (rated for 150 hp), but is it right on the edge and a couple of hundred extra pounds is enough to make the difference? I can live with it being a horespower issue if I have to. Pretty expensive to trade up I would think. If anyone knows of a good trade, let me know.

How about the max rpm? Seems like it's safe, if not a bit low. Too low? Will a prop change make a significant difference?

As far as a jack plate goes, will just setting the motor back a little help? The design of the boat means that the motor can't be lowered, and I don't know jack about jack plates!.

I'd really appreciate some advice from some folks who have some knowledge on set-up. Thanks for your thoughts and help on this! Eric

 

[stratos21xl]

it's an experimental process at best. In general a prop can raise or lower the rpm's a motor will turn depending on the number of blades the prop has ( 3 or 4 ) and the pitch or rake of the prop. A jack plate is nice for having the ability to raise or lower the motor and this will definately affect the rpm's. How heavy is the boat? What brand and pitch prop are you currently running? I would recommend a chat with Wrenchin2 or give the guys at performance props in soddy a call. If nothing else call the boat manufacturer and see what they recommend. Another big help when chosing a prop is knowing the gear ratio on the lower unit/crankcase of the motor.

 

[JDK]

a stainless prop will help some for sure.. it did on my boat.. sounds to me on a big heavy boat like you have it is just under powered you be amazed at what a 150 would do for that boat

 

[SpurHunter]

If needed I can post the video I took of a few weeks back while in the boat with four passengers too Eric. Surely SOMEBODY can give you some advice here.

 

[wrechin2]

If you drop pitch in prop it will generally do 2 things.

1) MOST of the time it will raise the RPMS. There are sooooo many characteristics when it comes to props. I have seen ,on the same set up, a 23P will turn more rpms than a 21P. On a set up I had, I could turn a 26P chopper to 6K but only able to pull a 21P laser to 5500. The chopper lifted more of the boat and the laser couldn't so It was like I wasn't even trimming it. Hope this makes sense.

2) a smaller pitch would allow the engine to spool up quickler and have a better hole shot. Similiar to pulling out in 2nd gear in a manual transmission and then down shifting to 1st.

Tim and Billy over at Performance will work with you and may be able to get you where you need to be.

As far as a jack plate, if it porposes badly now, a jack plate may add to it and make it worse. It will change the center point of balance but will get the prop in different water and may help in that aspect. Like said before, it is a trial and error issue.

 

[Guest]

eric m , there are a couple things you may try the least expensive is a simple whale tail bolted to cavitation plate lots of big H/P boats are running them now for stability and hole shot issues . then if that does not solve the problem try some transom wedges. they bolt between the motor and transom and change the trim angle.

 

[SpurHunter]

What gets me on this is how bad it cavitates. I keep going back and forth thinking its the prop.....

 

[Fat Albert]

<font color="#ff0033" size="4" face="comic sans ms,sand">Eric, you know that I love ya........ loose weight and pull Spur behind on an innertube......FA</font>

 

[Bubbakat]

Get some one to lay on the ground and look to make sure there ain't a hook in the bottom of the boat. Check the prop to make sure it ain't slipping. It sounds like the prop is running in air bubbles in the water and can't get a grip.

 

[SNUFFY]

i`d say the tunnel hull may be creating a weird set of waves ..... I`d talk to somebody that has some experience with it. I`d say it`s totally different from standard boat hulls. Part of the reason for jackplates is to get the prop back into less disturbed water from the hull....with a tunnel I don`t know.

 

[wrechin2]

Props can make a huge difference in the ability to keep a "bite" on the water.

There are several different styles of tunnel hulls. Sometimes the best thing to do is call the boat manufacture. They can ususally tell you what is best to run on that hull/engine combo. Just a thought.

 

[SpurHunter]

Its too bad a jack-plate cant be used in this situation, the stearing controls will not work if the motor is dropped, (hits the side-wells).
Sounds like testing some dfferent props might be in order first.

 

[wrechin2]

WAIT A MINUTE.......... Is this a boat with a 25" transom with a 20" engine???????????

 

[SpurHunter]

No its not james.

 

[willyb]

Eric i have the same motor on my boat other than mine is a 01 model 90 Honda. My boat is a 96 challenger 18 FT bass boat with 20p stainless steel quicksilver laser 2 prop a jack plate. If i fill the tank up and the live wells up with me and my partner it is a pain in the a$$ to get out on plane. But if i just put a half a tank in it will get up on plane alright.I have played with the jack plate a little with no results. Trying right now to find someone with a four blade prop to let me put on to see if that helps (hate to go buy one and it not help) I think these motors just do not have the low end torque.

 

[Jason F-18]

I would agree with willyb, my 20HP Honda will push my boat with just me and an 80lb dog at about 25mph. As soon as I add someone light in the boat, my top speed drops to about 20mph. I have had three people one time and it could barely get on plane. I do think these four strokes just like being at higher RPMs, 've even read somewhere about someone having theirs up close to 7000. I have wondered what changing props would do to mine as well.