Modification of factory props

[stephens013]

I am planninga haul out in December and would like to check if any adjustment to the 22X2315four bladed props will give me any additional efficiency /speed/ economy?

 

[barlow]

If your vessel is performing to cat specs ie 2800 rpm WOT then jobs done. If props are further modified you will have either too many revs or not enough which will require further adjustment.

Its no more a black science than a rack reset. Various adjustments to cup and/or pitch produce predictable results when being carried out by an expert shop.

 

[osd9]

Stephen:
The 400DA is VERY similar in hull design to the 410DA. The CAT 3116-TA motors are also VERY similar to the 3126-TA motors.

The 410DA came from the factory with 22X23 Nibral props with a slight/medium cup on the outer edges of the blades. The CATs are spec'd for a WOT of 2800 RPMs. It is a generally accepted practice to prop these CATs to achieve a WOT of 2825 +/- 15 RPMs when FULLY loaded and with a clean bottom. You should make sure that all your CAT service is up to date and that you are reading EXACT RPMs from a RELIABLE source. The factory analog tachs are NOT going to give you exact/reliable readings. You need to either upgrade to onboard digital tachs (Aetna's) or purchase and use a handheld laser tach.

All that said, you may be able to save some time and expense by mimiking my experience with re-propping my CAT powered 410DA. At the very least, it's a good starting point for you. I spent the first three and half seasons tweaking my props. It was both time consuming and costly. However, the results are well worth it.

Here's where I'll disagree with barlow's statement that propping is "an exact science". Sure....Pitch and Diameter are exact and can be measured and repeated from shop to shop so long as they use the same type of equipment and scanning software. But....the cupping is where a lot of the 'magic' happens. And...all cupping is not the same. Some shops will cup just the tips...some will cup down the edges of blade ....some will adjust the cup as it turns the edges of the blades....etc...etc..etc... You can see where cupping can get very complicated.

I settled in having my props pitched to 22 X 22 with a custom cup that starts out agressively at the blade tips and then gets less agressive as it rounds the edges towards the hub. I can achieve 2845 RPMs with a fully loaded boat measured from digital Aetna tachs. Depending on condtions and loading I cruise generally around 2350 RPMs +/- 75 and will achieve 22-24 knots.

I hope this helps....

 

[topgun1185]

I agree prop tuning is a black science. I think the best performance tweek is props. many captains just disregard them. I seen then damaged by inproper intallation and removal never mind hitting something. I used a prop service in NJ that use "prop scan" it gives a computer digital read out of each prop. Although time comsuming and somewhat expensive a "tuned" prop really dials in the boat. You can feel the difference.

 

[stephens013]

Thanks to all.