HAMMER

30' Sport Fisherman   Boat building project

design and build of a center console offshore sportfishing boat 

                                                 

In hindsight, the Mercury's fit my hull design a lot better as their lower units are much more forgiving compared to the Suzuki's which have proven difficult to set up on this boat. The problem seems to be the Suzuki's do not stay hooked up at speeds over 50mph. The problem ,I think is the raised keel pad which may be lifting the props into the disturbed water that is exiting around the raised pad. Mercs did ok with this Zukes, not so much. One engine, usually the port, starts to ventilate around 50mph thereby stopping the engines from achieving WOT rpm. I tried a lot of different props, each with different designs and all had this same problem. I went back to four blade round ear's, and these worked the best so far. With the round ear, when the boat is light, I can trim the engines out past hull level and lift the bow and this allows the props to be buried enough to finally achieve WOT rpm. I did not find that the large OD (16"D) props worked well and the much smaller 14 1/4"D Turbo Ultima four blades have provided the best overall performance so far.

Now I am running a set of unmatched props, the port is a Turbo Fusion four blade 14 1/4 X 23P and the Starboard is a Turbo Ultima four blade 14 1/4 X 23P. These are about 1" to 1 1/2" too much pitch and probably a set of 21"P Turbo Ultimas would be the closest that I can buy to what I need.

        Turbo Offshore I 15x24P

  rpm    mph   %slip  mpg

3600     32      18.6     1.95

4000     38      13.1     1.9

4500     45       8.5      1.6

4900     50       6.6      1.4

5450     53       11      -

     PowerTech OFX 15 1/4X22P

4400   39.5   10.4    1.65

4600   41      11.0    1.58

4900   45        8.3    1.38

5900   52.5    11.2    1.1

Turbo Ultima 4  14 1/4X21P

3500    27      19.3    1.75

4000    36.5     4.0     1.8

4500    40.9     4.9     1.73

5500    50.8     3.4    1.33

"Pair" port Turbo Fusion 14 1/4X 23P  starboard Ultima4 14 1/4X23P

motor dropped to 1st hole.

3500    33        10.0%    1.97

4000    40         4.59      1.82

4400    44.4      3.6        1.62

4500    45.6      3.29      1.63

5000    50.9       2.8       1.36

5600    57.4       2.19      1.3   WOT achieved at last!!

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Last modified: October 27, 2011