Ribcraft 4.8 prop choice

[Ash Smith]

Afternoon guys,
New here, recently purchased a Ribcraft 4.8 with a 2002 mariner 60 4 stroke,
It’s currently running a 11, 1/8 diameter 13 inch pitch SS prob, it’s really quick into its plane even with a number of people in and easily hits the 6k Rom upper limit… I’m after going up in pitch but interested in what others are running? Usual load will be 2/3 adults in average… after a good all round prop for cruising… at the minute 2 adults and a toddler it’s sitting at around 20 knots at 4.5k, hitting maybe 28knts WOT, so far been recommended a Mercury spitfire 14 pitch 4 blade prop, although they only come in a 10.1 diameter?
Looking for suggestions and performance reports?
Cheers
Ash

[chipko]

Hi and welcome to the forum.

We have a 2016 Mariner 60 (not command thrust) four stroke on a 5m XS rib. Propped for towing we run a Mercury Black Max 10 1/4” x 13” pitch which tops out solo at around 31 knots and able to bounce of the limiter at 6000rpm. Also have another Mercury Black Max 10 1/4” x 14” pitch as a spare which tops out at around 34 knots one up.

Prefer the sharper hole shot and livelier feel of the 13” even when not towing at the expense of a couple of knots top speed. However the 14” feels more relaxed at 22/25 knot cruising speeds.

Think if three adults aboard was the default load then, at least on our boat, think the 13” prop would be my choice.

[Ash Smith]

Thanks for the response, notice that my current 13 inch prop is also nearly inch bigger in diameter aswell than what you are running, the majority of my use so far is me my miss and my little lad, the engine jjust seems to be running hard at a mid 20s cruising speed, I might be just expecting too much from
It after coming from a ranieri centre console with a 115 yam 4 stroke on,
Thanks for the reply !

[Swordfish]

Hi Ash, great choice of boat! Try the Mercury prop calculator using weight of the boat. It’s on the Mercury website.

I’ve been on a similar discovery journey recently. Three blade should have less drag, so if you are not struggling to get on the plane, experiencing chine walk or poor handling then I’d say stick with three blades. I’m currently running a ballistic three blade 21” race prop which is really a beautiful piece of engineering. At about 6,000 rpm I’ve had as much as 52.2 Knots. However, it’s pretty skittish at that speed and I wouldn’t take the kids out with me and run WOT. I’m going to try 4 blades to give improved control but I am dropping a half pitch to try to compensate for the drag and/or get the revs up a little.

I also ran the same boat with Yamaha 90hp two stroke and tried both a 17” and a 19” K series ally prop. Ran great with both but cavitated a bit more on the 19” but then it did have a much better top speed.

The above are quite different scenarios so do check out that prop calculator see what it’s saying.

[jonp]

On a zodiac 470 with a 2014 merc we are using a 12 x 14 vengeance prop which sits in the higher max rpm range with one small person but still achieves 29kts with 5 adults and and spearfishing gear. I believe top speed is around 35kt. I do have a smaller boat with a new Yam F115 which is fun!!!!!