31FlyCruzr
Active member
- Joined
- May 17, 2006
- Messages
- 130
- Hatteras Model
- 31' CRUISER (1967 - 1971)
I saw the post for larger props on the big Hatts and wanted to provide my recent experience on a smaller boat. I have struggled with the factory sized props on my 31 express cruiser. It is easy to calculate slip, which I was off the chart on, and it shows when trying to run in a swell, the boat boggs down and looses speed running upswell but rpms are steady. I could drop from 17 to 10 knots.
Looking at some old propeller nomographs from my father it was clear that I needed more blade area and less pitch. I was able to tell that the proper pitch for my existing cruise-boat -speed and engine rpm should be no less than 13 at optimal slip.
Factory props were 16 X16 3 blade, when I bought the boat it had 16 X 17 3 blade, and the seller warned me not to go back to the factory props as she would not run with them. He had added tanks and obviously weight with them for range.
That said last year I needed to run 3100 to stay on plane at about 17 knots.
Enter ebay, I found a set of 17 X13 4 blade props on ebay. Boat is now on plane at 2800-2900 and top end rpm is increased by about 200 rpm and several knots. Hatt's need blade area in the water and pitch that is efficient at the cruise speed. I need to run more and get her out in in swells chasing strippers this fall to be sure there are no drawbacks, but so far I am very pleased.
The purchase had me worried so I contacted the seller, he said the props were from a 33 Egg Harbor that had small block power. I have small block Chevy/crusaders. So I roled the dice. I do not know the gross weight, so prop calcs were an issue.
Looking at some old propeller nomographs from my father it was clear that I needed more blade area and less pitch. I was able to tell that the proper pitch for my existing cruise-boat -speed and engine rpm should be no less than 13 at optimal slip.
Factory props were 16 X16 3 blade, when I bought the boat it had 16 X 17 3 blade, and the seller warned me not to go back to the factory props as she would not run with them. He had added tanks and obviously weight with them for range.
That said last year I needed to run 3100 to stay on plane at about 17 knots.
Enter ebay, I found a set of 17 X13 4 blade props on ebay. Boat is now on plane at 2800-2900 and top end rpm is increased by about 200 rpm and several knots. Hatt's need blade area in the water and pitch that is efficient at the cruise speed. I need to run more and get her out in in swells chasing strippers this fall to be sure there are no drawbacks, but so far I am very pleased.
The purchase had me worried so I contacted the seller, he said the props were from a 33 Egg Harbor that had small block power. I have small block Chevy/crusaders. So I roled the dice. I do not know the gross weight, so prop calcs were an issue.
