how much can you do with prop options

hwsiii

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Jan 25, 2009
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Re: how much can you do with prop options

You are looking for a 0 degree rake prop for your boat, or even possibly a forward rake prop, to lift the stern higher, not the bow. When I have a chance I will run the numbers you have posted and give you a recommendation for the exact prop and manufacturer as well as the model.

H
 

limitout

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Oct 1, 2013
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Re: how much can you do with prop options

You are looking for a 0 degree rake prop for your boat, or even possibly a forward rake prop, to lift the stern higher, not the bow. When I have a chance I will run the numbers you have posted and give you a recommendation for the exact prop and manufacturer as well as the model.

H

thank you for all the help you are giving me.

sorry to be such a PITA but I just didn't know anything about what I "should" be looking for. I was expecting you to say I needed a 15* rake so I was prepared to buy the wrong prop again if you didn't help me out with this.
 

smokeonthewater

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Dec 3, 2009
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Re: how much can you do with prop options

remember also that the right prop for this boat will be wrong for the bigger one you are planning to get... it doesn't hurt to run numbers but you need to run em on the new boat before buying the prop
 

limitout

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Re: how much can you do with prop options

remember also that the right prop for this boat will be wrong for the bigger one you are planning to get... it doesn't hurt to run numbers but you need to run em on the new boat before buying the prop

point taken but the load will barely change (adding 100 lbs.) and the floatation is the same (hull width) so if anything its just giving more surface area to provide lift and a small amount of extra drag (but only when its in the water) so I would be shocked if it were different enough to require a different pitch. its a lot different then adding 2 feet to a fiberglass or other type boat where it is a dramatic change.
 

limitout

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Re: how much can you do with prop options

now I have more confusing data to absorb after talking to the guy at power tech about their props. it would appear that blade design or style can alter or even cancel out some of the affects of other dynamics such as rake

I called power tech and asked about a clever style prop which is advertised as having good stern lift and said to be designed for inflatables and flatboats.

when I called them to find out what the rake was on that prop, the guy says it still has the same 20* rake in it that my present prop has but because of the clever style blades it doesn't have the same down force of the full bladed prop that causes my bow lift issues. according to him the clever gives great lift even though it has a 20* rake to it because of its clever design and it should solve any bow rise issues.

then he tells me the prop I was asking about has too small a diameter to handle the horsepower of my motor and will have too much prop slip even though its listed as a prop designed to work on my motor and is said to be a good prop for inflatables and flatboats :confused: so he suggests I just get a 4 bladed version of the same exact prop I already have now even though that prop is causing too much bow lift :mad-new: (thanks for such a great idea mr power tech salesman)

so I guess the more I learn the less I know :confused:

what I think I learned so far about things to decide when buying a prop for an outboard:

pitch - the least of your concerns so deal with it last when everything else is decided
rake - very important but blade style changes how much influence this has on things
blade style - can be used to cancel out or greatly influence what effect the rake has
diameter - creates different characteristics in props but not anything we have a choice about for outboards
cupping - akin to and part of blade style used to cancel out or greatly influence what effect the rake has

so it seams there are just so many ways to get to a desired result from a prop that its hard to say there is anything to look for in design because if you concentrate on one aspect too much you can make a worse choice then if you chose without being informed.
 
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hwsiii

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Jan 25, 2009
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Re: how much can you do with prop options

limit, I tried to give you some basic knowledge about prop exhaust systems as well as prop rake and blade surface area. Props are not like tires on a car, although they both move objects of different sizes, weights and horsepower in a forward direction, and that is why I call it the black art of propellers.

I have tried before to give people more knowledge by explaining different prop characteristics and the effects it has on how a prop will theoretically react on a particular boat and motor, and it has not worked very well for me, as people find the explanations either too boring, they do not have enough knowledge to understand the principles involved or I am just not good at all in trying to convey knowledge and it is probably the latter, although I do have one that has over 7,500 views and I am very happy with that.

" limitout, as smoke mentioned "EVERYTHING done with prop design is a tradeoff "

" I had a very spirited discussion on here one time with 45Auto , who is extremely knowledgeable in the field of fluid dynamics, which is a subject that is beyond my base of knowledge. So I decided that I was going to put a lot of effort into learning what I needed to understand in order to use these complex equations, so I could utilize them to have a better knowledge in water flow on props and boats. After about 3 months reading theory and working with equations I finally figured out that I would have to spend years in order to gain the knowledge required to actually use them in any manner that would be useful in my applications, so I gave up. "

There are people here in the prop forum who have been helping people with questions about a better prop for their boat and motor for years and I will take this opportunity to name a few that I know of steelespike, smokeonthewater, and Texasmark. They had prop knowledge before they got on Iboats and as they have helped more and more people their knowledge has increased substantially over the years, and they do this for FREE, because they enjoy helping other people with problems and much less knowledge about propellers. And the two best prop Guru's that I ever knew on here were Dhadley and walleyehed, and their knowledge of props was just astounding, because they worked with them everyday for years and years, and I am so sorry that their knowledge and expertise is not available here anymore.


What I am trying to tell you is that if you really want to know about all of the idiosyncracies involved with props and their attendant relationship with any particular boat hull, weight and motor combination then you will have to spend more time than I did trying to learn more about fluid dynamics, and not give up.

" limitout: so it seams there are just so many ways to get to a desired result from a prop that its hard to say there is anything to look for in design because if you concentrate on one aspect too much you can make a worse choice then if you chose without being informed. "

And that is why people come to this forum, to get help from people who have more knowledge to help them pick a BETTER prop for their particular boat and motor and their particular uses and needs, not always the BEST prop by any means. Props are not cheap and buying the wrong ones and having to replace them because they don't perform the way you need them to can be very expensive.
 
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