Posts: 3508
Location: Elk River, Minnesota | Hiya,
First off, thank you for the compliment. 
In changing from aluminum to steel, you will generally see about a 200 or so RPM drop because a steel prop will flex quite a bit less than an aluminum in the same pitch and diameter. Now...in your case, you have a few more things changing, because you are dropping diameter by 1/4", which is usually an increase of 100 or so RPM. So...with just that in a 3 blade model, you would be down roughly 100 RPMs. It the trophy prop has some good cupping on the trailing edge as compared to the black max, so it could potentially reach a 200 or so drop in RPM.
Now...the trophy is also a 4 blade prop, so there will be another 200 or so RPM drop due to adding the blade. The reason this happens is due to the extra friction you are gaining due to more surface area of the prop in contact with the water. Given the height of your motor now, I would suspect you would see a drop of about 400 or so RPM from where you are currently.
BUT!!! If your motor can move up, you will gain some of that back without any loss of handling due to the 4th blade...with the potential of going to the highest bolt hole position and still have a prop grabbing quite well. It is possible you could gain back about 200 rpm.
Performance of the boat will be with handling more than anything. Hole shot might increase a little, but since you are turning the same pitch, I don't believe it will change to any significant amount.
With the 4 blade steel prop, you will have more control over trimming which in this case you will feel your entire boat might be lifted more from bow to stern, which is really nice because you can find a sweet spot where the boat will just feel like it is floating along on air..easy to control, and smooth.
Top speed will most likely drop a mph or two as your rpms will be down, but not enough that would make it a dog....
The best thing: mid rpm cruise. You should be able to stay on plane at a lower rpm level than you are currently finding due to the extra lift and blade. I'd guess you could still be on plane at 3000 or so rpm without too much issue (this is very tongue in cheek, though as much of this depends on what you are hauling as well...)
Worth a try, though...you might find it to be a nice improvement for what you are looking for.
Steve |
