Elevation change on prop selection?
 

Hi,

I have an 04 SC21 with a Merc 4.3 and Alpha 1 1:81 that is running a 17P 4 blade at the moment. It came from CO and was running at around 4700' elevation. This set up worked fine for the PO (Motto on here) and ran low 40s at recommended rev ranges with a good hole shot. He had problems with the 17P 3 blade that came with the boat when he got it and the change to the 4 blade sorted that for him. He gave me both props but I expect to have to change them due to my lower elevation.

I will be using the boat at between 1200 and 1500' elevation in southern NV in a mix of river and lake. My question is what is a good starting point to jump to? A search seems to suggest that most here go with a 19P 3 or a 20P 4 on this engine set up but I don't know if that is the best for my elevation? Would a 19P 4 be a good start maybe or should i just go for the 20P 4 and not worry about the elevation? The 20 seems a big jump from the 17 with its known good performance only a couple of thousand feet higher up? Not looking for the flat out best top end but good mid range cruising and reasonable hole shot for tubing and so on.

Thanks

Ian


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Re: Elevation change on prop selection?
 

Need to run her when you get a chance and see what the WOT is at 1500ft.
Need 4400-4800 rpm for optimum running.
I would bet on the 20P 4 blade , but don't hold it to me.:yes_grin:
For what your after , no matter what I'd stay with a 4 blade prop. You only loose a couple mph compared to a 3 blade , with a lot better characteristics for play / cruise mode.

Re: Elevation change on prop selection?
 

I'm gonna go with the 19" - 4 blade and would suggest an aluminum Mercury Spitfire prop. The reason i'm suggesting the 19" is because that 4.3 is going to have to work a bit to push that 21' boat and i think the 20" might be just a bit much for it. I also suggest the Spitfire prop design cuz it is a bit on the aggressive side so it should help in the performance.

You might also want to consider installing a set of Smart Tabs!

Re: Elevation change on prop selection?
 

+1 on smart tabs!
If you end up buying from a local shop lots of them will let you try the prop so you can get it dialed in. I'm curious to see what she ends up running down there!

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Re: Elevation change on prop selection?
 

Thanks Guys. Smart Tabs are high on the list but I want to get a feel for the boat before I put them on so I can compare.

I am looking to stay with a 4 blade probably to get the low end and mid range, just wasn't sure if I should get a 19 or the recommended 20 to start with and see how it handled. Think I will go with the 19. I am sure I will need to dial it in a little and maybe play around with a couple of different props but it sounds like the 19 is a good starting point.

Will keep the 17s as I plan to go play in Lake Powel now and again and that's closer to the elevation Moto was running at.

Thx

Ian

Re: Elevation change on prop selection?
 

There are some pretty reasonable props out there. I think that Solas 4 blade was under the 150$ mark from the boat shop.
I bet the 19p 4 will get you around pretty good.

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Re: Elevation change on prop selection?
 

Thanks Moto. Will get one, see what it does and let you know.

Re: Elevation change on prop selection?
 

Just ordered a set of Smart Tabs. SX10512-70 are what they recommended. Lake was a bit rough and had a lot of porpoising the other day, we'll see if they calm it down a little.

Having some welding done to the lower unit at the moment after finding the sandbar right opposite the boat ramp that everybody but me apparently knew about and taking a chunk out of it.... :(

Will have a 19P 4 Solas on it when I get it back as well.

Re: Elevation change on prop selection?
 

Good to hear you have her out on the water! You'll love those tabs. As for the skeg... Its only aluminum. Its fixable!

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Re: Elevation change on prop selection?
 

Skeg wasn't the main issue it was the large chunk missing off the cavitation plate.... :eek_animated:

Was just moving out from the ramp towards the entrance to the lake with the drive fully down and hit a sandbar. No warning buoys or markers!! Lakes so low they have given up trying to mark them apparently. Picked up a rock or something and it took out a pretty big chunk of the plate and half the brand new anode... Skeg was just nicked a bit. :(

Found a local Mom and Pop prop shop and he's welding it up and putting on the new prop I wanted. Hoping to get it back tomorrow so I can go get it wet over the holiday weekend.

He agreed the 19P 4 was a good choice for the new elevation. I'll just get the solas for now whilst I am still 'mapping' sandbars.... :yes_grin: