go easy.. please..

[glendale]

o.k. i am totally new to boating. i read th info that you need to help me and i am not sure i even know how to get all of it.

my boat is a 1967 dorsett with an iron duke four banger my outdrive is a mercruiser. that i am assuming is the original. i am looking for a little more top end. i think the prop is alum. i keep the r.p.m at about 3800 and it seems pretty slow. i went out and got these numbers off the prop. i hope they help.r.p. 17 a 15 and 48 65450a4. i will do my best to help out with any info i can. i have only owned the boat for a couple of days.

please bear with the new guy...

 

[180shabah]

Re: go easy.. please..

first - welcome aboard.

inorder to provide any useful suggestion we need more info. "keep the rpm at 3800" and "seems pretty slow" don't help us any. To match the prop to the boat, we need to know what it does at WOT - rpm AND speed(gps if possible). We also need to know the WOT spec for your engine.

Lastly - don't forget you have less than 100hp getting to the prop, so there may not be much to gain with a new prop.

 

[glendale]

Re: go easy.. please..

cool i will get that info as soon as i can. i have no gps so it will be a while.. thanks for letting me know what you need though.

 

[Silvertip]

Re: go easy.. please..

You've only had the boat 2 days and are already looking for propellers. Why not get the boat sorted out, tuned up, hull cleaned, and ensure that it is making full power before even thinking about props. And so you know -- the best prop is one that allows the engine to rev at or very near the manufacturers recommended wide open throttle rpm which in your case is probably around 4500 RPM with an average load. Speed will be whatever that prop provides.

 

[glendale]

Re: go easy.. please..

You've only had the boat 2 days and are already looking for propellers. Why not get the boat sorted out, tuned up, hull cleaned, and ensure that it is making full power before even thinking about props. And so you know -- the best prop is one that allows the engine to rev at or very near the manufacturers recommended wide open throttle rpm which in your case is probably around 4500 RPM with an average load. Speed will be whatever that prop provides.

because i love the looks of the boat. and it really needs nothing to be done. i have been a lot of custom cars so i know my way around. i am new to boating not engines. my thought was if i could make it a little faster i would dig it a little more. i understand i could have bought a boat with an eight or six. i was just looking for advise. and i feel i was very respectful. so why don't you calm down a bit? the boat has a rebuilt motor and out drive new interior.what should i be sorting out?

 

[180shabah]

Re: go easy.. please..

what to sort out? Right now, you are new to boating and yhis is a new to you boat: you have all kinds of ideas right now about how you will use use it. Cruising, fishing, skiing, tubing, etc......

Your actual usage will after a a year or so will likely be quite different from your planned usage. At that point you will be in a better position to make decisions about propeller styles.

You stated in your original post, you keep the rpms around 3800 and it feels slow. That is because it IS slow. Probably in the neighborhood of 25mph. WOT with that engine will probably fall right around 30mph at 4500rpm. A new propeller WILL NOT get you any more noticable speed. You are POWER limited.

 

[glendale]

Re: go easy.. please..

what to sort out? Right now, you are new to boating and yhis is a new to you boat: you have all kinds of ideas right now about how you will use use it. Cruising, fishing, skiing, tubing, etc......

Your actual usage will after a a year or so will likely be quite different from your planned usage. At that point you will be in a better position to make decisions about propeller styles.

You stated in your original post, you keep the rpms around 3800 and it feels slow. That is because it IS slow. Probably in the neighborhood of 25mph. WOT with that engine will probably fall right around 30mph at 4500rpm. A new propeller WILL NOT get you any more noticable speed. You are POWER limited.

cool thanks for telling me AGAIN that i don't know what i'm doing. how about this. i know what i am going to with the boat. so if i have offended you by asking about a prop in the prop section my bad. i will get the info that the other poster asked for and then get back to him. as for you how about we agree to disagree. i understand the boat will never be fast. i wanted a little more out of. and i kept at 3800 rpm because that is what i was told was redline...

 

[Andy in NY]

Re: go easy.. please..

cool thanks for telling me AGAIN that i don't know what i'm doing. how about this. i know what i am going to with the boat. so if i have offended you by asking about a prop in the prop section my bad. i will get the info that the other poster asked for and then get back to him. as for you how about we agree to disagree. i understand the boat will never be fast. i wanted a little more out of. and i kept at 3800 rpm because that is what i was told was redline...

no one is trying to tell you that you dont know what you are doing. they are saying that a prop most likely isnt going to net you more speed. you need to check the specs on that motor to determine what max rpms are and report back with that coupled with your top speed at WOT. that will tell if the boat is over or under propped, or propped just right.

 

[ExxWhy]

Re: go easy.. please..

Here I thought the guys were being gentle and helpful. You did mention you are new to boating. It seems reasonable to expect some very basic questions before you get any useful answers.

Your original post did not mention any engine experience, nor did you say fresh rebuild or tuneup, runs like a top, etc. That is the first thing to verify before any prop discussion as they rightly pointed out. Glad yours is sorted out in that area. It would be most helpful for you to find out exactly what the recommended max RPM is. Might need a service manual to get that info for your specific combination, I wouldn't rely on " I was told" or even the knowledgeable approximations the guys gave you. Find it in writing someplace from the manufacturer if you want to optimize your setup. No doubt you will get a lot more speed if you can run the motor up to the max speed it is designed to run at.

I think the experienced ones are telling you correctly that what you think you want to do be able to do with the boat today may not be the same after you've had it for a while. How much load you want to be able to carry, tubing, fishing, just cruising, whatever. At any rate, for now are you looking for absolute max top end with one person or do you want a better hole shot with 4 people aboard? You won't get that from one prop. It's an either/or compromise.

As the stickies say, you need to know a few numbers first to get any useful information from the guys who know what they are doing. Their recommendations are only as good as the info you give them. So relax a bit, be happy someone more experienced is willing to help.

Nobody is trying to pick on you, except for me with this last comment. There is a key on the keyboard called "SHIFT" and it's used to make small letters big. Quite a useful tool of the language for the last thousand years or so. Yes, I am a dinosaur, and yes I am just busting your chops a bit in fun.

 

[Tail_Gunner]

Re: go easy.. please..

Greetings...A few things if 3800 is your Wide Open Throttle...WOT with what appears to be a 17p prop you have some issues..Like SilverTip says 4500-4800 is probably the true rpm band..You can always take a quick peak in the I/O forums to establish what it really is..

The boat is new so first establish that the tach is actually reading correctly...Boat tachs a not very acccurate as a whole...Could you tell us the length weight and type of boat it is.... such as a 18' cuddy or 25' cabin

Turning a engine on a boat is a bit different than a car..you have one gear and that needs to geard with a prop that will run the boat from 800 rpm to the top of its designed rpm band. While under propping will not hurt a boat...Over propping will shorten a engines life considerably

Youve found a great site...There is enough info here that you can do literally anything you mind thinks of...It can become a bit of a problem if your not careful

 

[180shabah]

Re: go easy.. please..

cool thanks for telling me AGAIN that i don't know what i'm doing. how about this. i know what i am going to with the boat. so if i have offended you by asking about a prop in the prop section my bad.

If the above post is all it takes to get your thong all twisted up, might be time to go put on your "man britches"

i will get the info that the other poster asked for and then get back to him. as for you how about we agree to disagree.

not payin' real close attention, are we. that other poster was ME!!!

i understand the boat will never be fast. i wanted a little more out of.

A little more is exactly what you will get - very little. You can change certain performance characteristics, acceleration, minimum planing speed, blowout etc, but in this class of boat(size, weight, power) you just won't see any more speed from a simple prop change.

and i kept at 3800 rpm because that is what i was told was redline...

Since a boat doesn't have a redline - it has WOT spec - which is a range, NOT a single RPM, you might want to verify this in your factory service manual...

 

[glendale]

Re: go easy.. please..

I understand what all of you guys are saying. i am not upset at all. i belong to alot of forums. i will get the info asked for and start a new thread at that time.i agree this seems like a great forum and it's very informative. thanks for your time...

 

[walleyehed]

Re: go easy.. please..

glendale, 99.9% of the folks here will be helpful...Please keep in mind it's real hard to determine a person's demeaner with just words read on the net so don't put too much into what "may" appear sometimes to be a hard-core answer. Some of the most knowledgeable folks in the industry are a part of our forums so hang tuff!