What prop for Parker 630 w/ Optimax 135

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Hi folks,
We have acquired a Parker 630 with an Optimax 135 Saltwater. At the moment we have a Stainless Steel 3-blade on her and she performs well, however we want to switch to an aluminium prop as the boat will be used for training.

There is no identifying marks on the Prop with regards to diameter/pitch.

Could anyone give an idea as to what diameter/pitch prop we should go for? We are more bothered about cruising and economy rather than acceleration. We would generally run with 4 people on-board. The boat has 4 jockey seats and wide console, nothing else extra that would add weight worth while talking about.

Thanks in advance

[Downhilldai]

I run a 150 opti on a slightly smaller RIB, but it's probably around the same weight. This boat runs ok with a 21" Laser II stainless prop. The 135 Opti has a lower ratio lower unit (2.00:1, as opposed to 1.87:1 on the 150), so with the slight reduction in power, a 21" pitch would probably be ok for your set-up, given the loading and focus on cruising.

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Thanks for the info