4 bladers are great for torque i.e. a heavy boat that needs thrust quickly. Like a dive boat or someone who carries almost max payload of say freight.
We fitted one and havent looked back. The performance is not the same for similar sized 3 blader. We took the advice from Steel Developments and it was very accurate.
For our application as a dive boat the only question I might ask other dive boats is why they havent got a 4 blader fitted. That said as yet I've not seen many 4 blade stainless props which would be the next logical but expensive step for us.
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New boat is here, very happy!
Simon www.luec.org