prop shape help....

[kfxguy]

I have an m645 prop that just kicks every other props ass. No matter what. I just did an X646 to try and beat my m645. Nope. It's about 4 mph slower. I detounged the crap out of it but maybe not enough. I tried an abc 1816 and it was horrible. Think I screwed it up anyway. Not worried with that one, it ended up at like 41 mm cuz I slipped on the belt sander lol. Anyway, look at the tongue difference. Should I cut the X646 down even more like the m645? M645 on right. X646 on left and abc on the rear.



The X646 is just much nicer and you can tell it's thinner. Just more tongue.

[srislash]

I would put a piece of masking tape over the M645's leading side and trim it to the outer shape, then pull it off and match it up on the 646. Make sense Trav?

[kfxguy]

I would put a piece of masking tape over the M645's leading side and trim it to the outer shape, then pull it off and match it up on the 646. Make sense Trav?

Excellent idea! Thanks!!!

[srislash]

Also works well to copy for reverse rotation such as say,,, 447's.

You can use the trailing edge and hub of prop as the reference guides.

Just where I came up with it. Oh and of course, balance after

[raptor347]

That M645 looks like it may have some extra cup bent in the TE. If so, the x646 will have a hard time keeping up.

[urbs00007]

That M645 looks like it may have some extra cup bent in the TE. If so, the x646 will have a hard time keeping up.

would it be a good idea for kfx to cut the 646 to the exact blade size as the 645 and remove cup if any then run? whats his next move if the 646 is slower than 645? is he rapidly approaching his boats max speed? this a good thread as kfx is putting alot of effort into this project and everyone can learn from the experienced boater's input.

[Fluid]

Removing cup will slow the boat...just the opposite of what the OP wants. Matching the exact blade area is less important than increasing the TE cup. Otherwise he is simply duplicating the m645 (with a tiny bit more root pitch), what's the point? Get a pair of jewelers pliers and bend in some cup.


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[urbs00007]

prop

Removing cup will slow the boat...just the opposite of what the OP wants. Matching the exact blade area is less important than increasing the TE cup. Otherwise he is simply duplicating the m645 (with a tiny bit more root pitch), what's the point? Get a pair of jewelers pliers and bend in some cup.


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he said he lost 4 mph with the 646. then someone said the 646 had more cup than the 645. so wouldnt cupping the 646 increase the load, slowing the boat even more?

[Fluid]

Read Post 5 again, the m645 has more cup added. That is probably why the x646 is slower. That, or he tested the props under different conditions. That alone can cause a 4 mph difference even with the same prop...


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[srislash]

Read Post 5 again, the m645 has more cup added. That is probably why the x646 is slower. That, or he tested the props under different conditions. That alone can cause a 4 mph difference even with the same prop...


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Just a light chop can really break a boat free. That can come from just a good sudden breeze over water.

[Fluid]

As big a difference is battery condition. A 100 degree battery will put out more voltage than a 75 degree battery will. Testing a prop with a battery fresh off the charger then comparing it to one with a battery half discharged can mean a difference of a volt or more....why bother. I see many folks making these mistakes every day, getting meaningless "data" and often choosing the wrong prop or strut setting because of it.



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[kfxguy]

I made several passes with both props. Swapping back and forth between the two. I went the same direction every time. I put the m645 on, made one pass. Brought in. Checked speed. Swapped prop to x646, made pass. Brought in. Checked. Slower. Put m645 back on. Made pass. Check. Back to where it was on the first run. X646 back on...you get the picture. I'm not sure how I could be more consistent. The X646 runs 78.something every time and the m645 run 82.something every time. I thought it was a consistent test?

[Fluid]

Wait, 646 or 648? Now the OP says both...typo? No one said the OP's testing was not done well, just that no one knew. It sounds like very good methodology to me. The difference is likely the lower thrust from the larger prop compared to the cupped 645. Forget blade shape and bend in some cup. Blade thickness matters too.


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[kfxguy]

Wait, 646 or 648? Now the OP says both...typo? No one said the OP's testing was not done well, just that no one knew. It sounds like very good methodology to me. The difference is likely the lower thrust from the larger prop compared to the cupped 645. Forget blade shape and bend in some cup. Blade thickness matters too.


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Sorry about that. Auto correct on my phone has the 648 stored lol. I didn't go back and fix it. Just for clarification I'm testing the X646 vs m645 back to back. I looked closely (the pic fools you, the X646 has a touch more cup, thinner and a bit more tongue. I'm reshaping it like the m645 to see if that helps.

[kfxguy]

Here's how much I had to take off....