Prop'ing a '81 Glassmate

[Handegard]

Both the props I got with my dads boat are just destroyed.

I bought a Quicksilver 15R17 today, to replace one of the two I have. Before I go out and use it, I wanted to come here. The other one I have the markings were no longer legible.

I planed to use it, tell you guys what my top speed, RPMs, and power was like, and then use that data to help choose a 2nd, more specific prop.

Is that a waste of money? Can we choose the ideal prop without me having another prop to baseline with?

It's a '81 Glassmate (Got a M shaped hull) with a Volvo AQ120B/270.

 

[Bondo]

Re: Prop'ing a '81 Glassmate

Can we choose the ideal prop without me having another prop to baseline with?

Ayuh,... It's hard to see where you wanta be, when you don't know where you're Startin'....

 

[Handegard]

Re: Prop'ing a '81 Glassmate

Ayuh,... It's hard to see where you wanta be, when you don't know where you're Startin'....

Had to ask For all I know, one of you has a book laying around that says what I'm supposed to have...

Next question.

If I know what I have for a 3 blade prop (15R17) would I just buy the same number if I went with a 4 blade prop, or would I need to experiment as well?

Thanks

 

[Silvertip]

Re: Prop'ing a '81 Glassmate

You apparently didn't read the READ THIS FIRST sticky at the very top of this page. Next, you need a baseline to determine whether what you have is correct and if not, what is the best direction to go. So far you are all over the map - two props, three blade, four blade, and you haven't even mentioned stainless or aluminum. The best prop is one that allows the engine to operate at or near the upper end of the manufacturers recommended rpm band. Since we have no idea what the OBSERVED WOT rpm is currently, there is no way anyone can help you. Lastly, there is no such thing as a "standard" prop for anything other than a small outboard. Engines aren't even shipped with one since the manufacturer has no idea what boat (v-hull, barge, pontoon, flat bottom, etc) the engine will be installed on. Each boat type and the load it carries dictates what prop is needed. So I suggest you use whatever prop is in the best condition and do your baseline testing with what you consider will be an average load. Average load is rarely one person so get this settled at the start and then keep the same load throughout testing.

 

[Handegard]

Re: Prop'ing a '81 Glassmate

Thats because your assuming. I did read the sticky. They didn't cover a single one of my questions.

I wasn't asking you to make a recommendation for my boat. I was asking if it was possible to determine a good prop without buying one just to try first.

I understand that WOT RPM is important, and what info I need to give you guys to get a recomendation. Again, I wasn't actually asking for a recommendation yet. I was asking if I was wasting money by buying a prop just to baseline.

I know the same outdrive/motor came with dozens or hundreds of hulls, but somewhere out there there is a book that says what *my* boat came with. Do any of you have it? I doubt it. Does it hurt to ask? I guess so.

Maybe if you read my posts without assuming I'm a idiot asking you to pick a prop for him you'll realize I just asked a series of random questions I had, that all have to do with propellers, (in the propeller sub-forum none-the-less) to better educate myself about propellers in general.

Do I know if pitch would change when going from a 3 blade to a 4 blade? Is that a stupid question? I google it and found no relevant results. I meant the question in the most literal sense- If I have a 15x17 3 blade, would a 15x17 4 blade be equivalent? I'm not asking you if it's better for my boat, I'm asking if it's equivalent, because I have no idea! I'm just trying to learn here, give me a break.

 

[Bondo]

Re: Prop'ing a '81 Glassmate

I meant the question in the most literal sense- If I have a 15x17 3 blade, would a 15x17 4 blade be equivalent?

Ayuh,... Relatively speaking,... Yes...

 

[Handegard]

Re: Prop'ing a '81 Glassmate

Ayuh,... Relatively speaking,... Yes...

I probably don't know enough to even formulate a question like that, so we'll call it even

I found a cheap prop on craigslist, it's in perfect shape, but not the same as either of what I have, 14x21.

Can I just use any prop to baseline (like the 14x21) or do I want to start with a prop that is already more closely matched to my boat, like the 15x17 I have (my dad had a 15x17 on it before, but not for towing) ?

Thanks alot, and have a great day

 

[hwsiii]

Re: Prop'ing a '81 Glassmate

Chris,
You might try reading this for a better understanding of changing props for better performance, and for the major differences between aluminum props and stainless steel.

http://forums.iboats.com/showthread.php?t=369057

My recommendation to you would be to go to a prop rebuilder shop and try to buy a used prop with the right to try it and if it is not right bring it back to try another one, then we can find you a better prop that you can buy new.

And don't be quite so defensive, these people are just trying to help you, but they just don't have enough information. 90% of the people that come here don't give anywhere near enough information for us to be able to help them, just look at the posts.

If you would rather do it without buying a trial prop I have a form that if you will fill out for me I can help find a better prop without having to do that.

And I would recommend you NOT buying the 21" pitch prop.



H

 

[Handegard]

Re: Prop'ing a '81 Glassmate

Chris,
You might try reading this for a better understanding of changing props for better performance, and for the major differences between aluminum props and stainless steel.

http://forums.iboats.com/showthread.php?t=369057

My recommendation to you would be to go to a prop rebuilder shop and try to buy a used prop with the right to try it and if it is not right bring it back to try another one, then we can find you a better prop that you can buy new.

And don't be quite so defensive, these people are just trying to help you, but they just don't have enough information. 90% of the people that come here don't give anywhere near enough information for us to be able to help them, just look at the posts.

If you would rather do it without buying a trial prop I have a form that if you will fill out for me I can help find a better prop without having to do that.

And I would recommend you NOT buying the 21" pitch prop.
H

I'm sorry if I'm a little defensive, I've consistently had a less than pleasant experience with this forum since I joined. I get that people come here and ask the world without even telling you what boat they have, but I've repeatedly asked questions on this website, only to have people jump on me after mis-interpreting my questions, which are always quite literal, or on the flip side, mock me for buying a bayliner, or a cobra, or whatever it is I asked about.

But- I also get some genuinely knowledgeable responses, and thats why I keep coming back. I'm very grateful to these of you that read my question, and respond with your opinion (or fact!)

I will pass on the 21 pitch prop. I don't mind the "trail" prop. My dad had the same one, he used it whenever he wasn't pulling a skiier. So I know I'll get use out of it, but I'm more eager to get the "other" prop, whatever it may be.

I do love the rebuilder idea. I have no idea where to even begin, but I'll ask around.

Again, thanks for the help,
Chris

 

[Silvertip]

Re: Prop'ing a '81 Glassmate

OK so you read the sticky. Good for you but it apparently meant nothing to you otherwise you wouldn't have to ask if buying another prop to establish a base line is a waste of money. Off course it is. You said you just bought a 17P prop. Why would you buy other on since that would be as much of an unknown as the one you have. Run the one you just bought since that would establish a baseline. You make changes based on that prop. No --there is no book laying around that tells you what prop is needed on what engine on what boat, carrying what load. There are too many variables for that. Some prop calculators can get close but there is no guarantee that calculation is spot on. That is also why engine manufacturers do not ship props on engines. It is up to the selling dealer to make make prop recommendation based on his experience selling that boat and "working with a good baseline". When individuals re-prop their boats they have to go through the same process and that is called "trial and error" or "establishing a base line."

As for getting "jumped on", that is not the case and is one of the problems with participating in a forum. One cannot always tell true intent in the written word and sometimes that gets misinterpreted. My suggestion that you didn't read the sticky contained absolutely zero ill intent and I think I covered in detail the reasons why the a baseline was needed. One thing we are not are "mind readers". If you need more information on props there is enough reading on the internet to make your eyes bleed. All you need to do is search "marine propeller theory" or "marine propeller principles" or similar search phrases.

If you feel you are being jumped on, then you need to look in a mirror as that can mean you are coming across as way too sensitive and perhaps don't care for an answer that may imply that you don't know as much about an issue as you think you do. When you ask a question, be prepared for answers you like as well as those you don't.