boat performance?

[1987 175 mercury]

I have a 1987 18.5 Stratos vt rocket bassboat with a 87 175 mercury on it.I will soon be changing the current set up trying to achieve the boats all around best performance.I have recieved excellent advice on setting it up but need futher knowledge in understanding it.I believe that i will be trying gain as much performance as I can by raising the engine heigth to keep from having to trim completely out and loosing the boats stability in the water.I also wonder if by raising the engine heigth will take away the boats ability to handle rougher water.I know that ultimate speed will be achieved by trimming out.My assumption is that I will be trying to find that sweet spot of engine heigth that at completely trimmed out allows my engine to run at its maximum rpm's at full geared and fuel weight,when lighter I will have to only run at the maximum rpm's.My boat is equiped with a HiJacker jackplate (not hydraulic) with a 5 inch set back.My current set up still has 5 inches of adjustment that I could raise the engine heigth with.When light I can get 5750-5800 rpm's fully trimmed with my set up now.I uderstand that there are still many variables yet to discuss.Assuming that I will adress water pick up issues,and prop issues.

 

[oops!]

Re: boat performance?

hi.....welcome to iboats...

i think your best approach right now.....is to set the height....

then spend a lot of time in the prop forums....i think the prop choice is your best bet for what you want

 

[1987 175 mercury]

Re: boat performance?

So,trying to understand what your recomending,are you saying that i should set my engine heigth as high as I can and still be able to pickup water when the boat is light and completely trimmed out?Then find the prop that will give me the performance that I need.From allready running this boat I understand the needs that this tunnel hull has and how important the bow lift is to get air under the hull.In my mind I cant help but think that I can achieve that by the engine heigth and prop without having to completely trim out and loose stability in the water.Am I wrong in thinking that way?

 

[Frank Acampora]

Re: boat performance?

As stated above, you will probably be best served in the prop forum. Perhaps send a message to Dhadley. But, understand--over at the prop forum they will want to know everything: prop size now, RPM, top speed, boat weight, etc. Save some time and give them everything you know.

Personally, I would start with testing props and when the best is found, then I would experiment with engine height.

Props come in bow lifting, stern lifting, and total lifting styles.

Getting air under the bow is a risky proposition: Too much and she will blow over on you. Unless there is big prize money in it for you go conservative.

This little tunnel hull has done it three times and I don't have a jackplate on it.

 

[mommicked]

Re: boat performance?

I'm no expert, but if your talking about "stability" in tight turns, I've heard some V-hulled tunnel hulls will lift part of the tunnel out or almost out of the water if they lean over far enough at high speed in a tight turn, and this can cause instability and prop slip. But I am no expert!

 

[cyclops2]

Re: boat performance?

Tunnels are the best on smooth water & going in a straight line.

You are wise to worry about rougher water handling. That is why many good tunnels DO HAVE a hydraulic or electric lifting jack plate setup.

I am 1 hour from the launch. RATS! I can not safely crawl back there & lower or RAISE the motor as choppy water conditions require.
Worse than RATS !!

 

[Bamaman1]

Re: boat performance?

Sorry, but this question is about using motor heights to get the best performance out of his boat--not tunnel hull boats (another issue.)

Boat performance might not be just an issue of 100% maximum speed. You have other issues, like handling, acceleration, ride that comes into the equation.

For example, my friend had a 13' Allison boat with 100 hp Merc (in 1972) that we would climb out on the nose to get the prop to quit cavitating. When it hooked up, the boat skipped across the water--beating you to death. It was blazing fast, but total performance was not there.

You have a very common boat hull, and a lot of people can give you good advice on such a boat. You might talk to a prop shop to see what propeller they suggest for your given hull and motor. Maybe they can loan you different props to try out. Remember that your Merc. 175 Black Max is comparable to today's 150 hp--they're now using prop horsepower instead of horsepower at the power head.

Your ultimate performance will be a balance of using the right propeller and experimenting by adjusting the motor up and down--to find the best compromise for your use. It'd be nice to have a hydraulic jack plate, but they're $1K installed.

Good luck!

 

[mommicked]

Re: boat performance?

My bad, I did'nt know this had been discussed on 1-1-12 in another thread. I also assume 3, 4 or 5 blade props would perform best at different fixed motor heights on this model boat?. It appears to be a high performance boat hull modified into a heavier bassboat layout. But again I'm no expert.

 

[ondarvr]

Re: boat performance?

His motor is rated at the prop.

It will be a combintaion of raising the motor and the right prop, different props can run at different heights, so you can start by raising it, but it may need to be changed again when you start trying different props.

 

[cyclops2]

Re: boat performance?

The original poster HAS STATED the boat has a tunnel. Not a V hull.
Tunnels have no large depths to play with. You either get it very right or you can have a real dog wasting lots of power all the time.

 

[1987 175 mercury]

Re: boat performance?

Thanks for all the insite into the issue.All opinions are very much apreciated and all helping me learn.The hull is a tunnel hull with a shallow vee.It is a unique hull to bass boats and handles speed and rough water well.The plusses that i have learned from it is that it does not chime walk when trimmed out.It also has a large set back with the transom design giving it clean water.

 

[cyclops2]

Re: boat performance?

That is a different hull shape. It is close to being a shallow TRI HULL in form. You would definately like the ease of a powered "Jack Plate" to adjust it while running.

 

[mommicked]

Re: boat performance?

I think the V in VT "stated" V hull w a short tunnel at the stern of the boat, and I've seen a few boats like this. They do not perform the same as true "tunnel " hulls, But again i'm no expert, I did stay at a Holiday Inn last night though Probly get good advice from the Scream and Fly crowd like before If all out perf. is wanted w this.

 

[juneeci]

Re: boat performance?

I also have a 1987 18.5 Stratos vt.

 

[1987 175 mercury]

Re: boat performance?

Have you had the boat long.If so will you share experiences with it.