First time boat owner with some questions...1998 Starcraft 1810 Bowrider w/ 4.3l Merc

[winnipegjohnston]

Hi all! I just turned 30 and was finally able to (allowed by the wife to) buy a boat. I found a 1998 Starcraft 1810ss bowrider 4.3l merc in great condition and picked it up! I have 3 kids and I'm really looking forward to this summer and boating with the family.

So I took the boat out this weekend for the first time and I have a concern about the RPMs. At WOT I'm only running at ~4k rpm and ~40mph. I have a 19degree prop. According to what I've read, my motor should be running at 4.4k-4.8k rpm and I should have a top speed closer to 50mph. I'm just curious as to why I'm not hitting my high end rpm? What do you guys recommend doing/checking? I was thinking about adjusting my throttle cable, but I don't want to mess anything up. Is a 19degree propellor "stock" for my boat? Could this effect my RPM? Any and all input is greatly appreciated. Thank you in advance.

 

[Don S]

Re: First time boat owner with some questions...1998 Starcraft 1810 Bowrider w/ 4.3l

There are a number of things that it could be. But since this is a new boat to you, are you using the trim at all?

 

[winnipegjohnston]

Re: First time boat owner with some questions...1998 Starcraft 1810 Bowrider w/ 4.3l

There are a number of things that it could be. But since this is a new boat to you, are you using the trim at all?

Yes, I have the trim all the way down during "launch" and then trim up when I'm on plain. I trim up to the point just before the boat starts bobbing. I tried messing with the trim with little results.

 

[Bondo]

Re: First time boat owner with some questions...1998 Starcraft 1810 Bowrider w/ 4.3l

Ayuh,... Welcome Aboard,....

A general Tune up, 'n Service, along with a compression test will give ya a solid baseline to see what her potential is...
Also,...
Up in the Adults Only section at the top of this forum is a "How To" thread about Not bein' able to achieve the proper rpms at Wot...

 

[winnipegjohnston]

Re: First time boat owner with some questions...1998 Starcraft 1810 Bowrider w/ 4.3l

Ayuh,... Welcome Aboard,....

A general Tune up, 'n Service, along with a compression test will give ya a solid baseline to see what her potential is...
Also,...
Up in the Adults Only section at the top of this forum is a "How To" thread about Not bein' able to achieve the proper rpms at Wot...

Thank you for the warm welcoming! So I found that thread with things to check for low revs at WOT. I'm not sure where to start... Well I guess my first question is what would be the proper propellor pitch and diameter for my application? Second question is what compression should I be seeing...somewhere around 60?

 

[fossill]

Re: First time boat owner with some questions...1998 Starcraft 1810 Bowrider w/ 4.3l

Preferably anything over. 100 psi.
At 60 you got big problems

 

[Bondo]

Re: First time boat owner with some questions...1998 Starcraft 1810 Bowrider w/ 4.3l

Thank you for the warm welcoming! So I found that thread with things to check for low revs at WOT. I'm not sure where to start... Well I guess my first question is what would be the proper propellor pitch and diameter for my application? Second question is what compression should I be seeing...somewhere around 60?

Ayuh,... Compression #s should be around 130psi to 160psi...

There's no such thing as the Stock prop...
It's whatever pitch yields the right rpms at Wot...
That's why you access the motor 1st...

 

[mkast]

Re: First time boat owner with some questions...1998 Starcraft 1810 Bowrider w/ 4.3l

Have you taken this boat out alone?
Did it have a full tank of fuel plus a wife and three kids and gear.
Lose the extra weight and see how it runs.
What is the condition of the propeller, even small nicks can drop propeller efficiency by 10 %.

 

[Brewman61]

Re: First time boat owner with some questions...1998 Starcraft 1810 Bowrider w/ 4.3l

With the prop you have, assuming it's balanced, etc..,, you should be in the ballpark to hit your WOT numbers.
Assuming your tach and speedo are accurate- boat speedo's can be all over the place accuracy wise.

 

[winnipegjohnston]

Re: First time boat owner with some questions...1998 Starcraft 1810 Bowrider w/ 4.3l

Arrrr...I meant to put 160 for compression. Okay, I'll do a comp test on it this weekend and see where I'm at. That's easy enuff.
When I went out I had a full tank of gas = 100litres. I also put in 91 octane (premium). I just had two passengers, so not a fully loaded boat by any means.
My prop does have a few bends/dings on the fins...nothing major but I can see it possibly reducing effeciency.
I'm pretty confident in my speedo and tach readings as I was driving with 2 other boats that max out at ~35mph and I was pulling from them but nothing mind blowing. The RPM seems consistant with my top speed so I would venture to say that those gauges are working.


Another piece of the puzzle I forgot to mention. The boat came with a hydro foil on it...Stingray MKIII). From what I've read this is supposed to help the boat plane faster and increase fuel mileage. Could this make my RPMs run lower? Would top RPM/Speed be the trade off for faster planing and better MPG?

Thank you for all of your responses. Please keep them coming.
Scott

 

[LSUJKer]

Re: First time boat owner with some questions...1998 Starcraft 1810 Bowrider w/ 4.3l

I want to offer my opinion, it's not your prop. Keep looking for engine issues.

I'm also a new boat owner. Just purchased a 1999 Starcraft 1810 lx with the 4.3. I'm running a 21p high five prop. Full tank of fuel, 6 people and I hit 4800 rpm in a few seconds, I actually have to back out. Not sure of top speed but will run with most jet skies. Had compression test run, 180 to 185, all cylinders. Your sterndrive might be geared different. Good luck.

 

[Dryon]

Re: First time boat owner with some questions...1998 Starcraft 1810 Bowrider w/ 4.3l

First I wouldn't rely on the dash tach......Hookup a real tach for a true reading.