Twenty foot owners

[Tuna Man]

I have recently read a member here was having troubles with his newly purchased boat (208 I think). We recently ran a few tests and I hope our results will help others.

2002 Grady 209 with every option available (T-top with curtains, freshwater shower, livewell, baitwell, leaning post, full cushions, etc), except raised bow rail. 2002 Yamaha 200 HPDI. Bottom paint in good condition. 2- group 27 batteries.

Test 1 13-3/4 x 19 Yamaha black stainless prop (original), engine mounted two holes up.
Boat loaded with sixty five gallons fuel, four people (800lbs), safety gear and minimal other stuff.
WOT - 43.5mph at 5300 rpm

Test 2 same setup as Test 1, but engine raised four holes (top hole)
Boat loaded with sixty gallons fuel, one person (200lb), safety gear and minimal other stuff.
WOT - 46.0 at 5400 rpm, boat steered a little better at cruise and prop still did not blow out

Test 3 15-1/2" x 19" Yamaha Saltwater Series II, engine on top hole
Boat almost empty, twenty gallons fuel, two people, safety gear, etc
WOT 49mph at 5600

Test 4 same Test 4, but full fuel (80 gallons), 800lbs people, 8 fishing poles, lots of tackle, food and drinks, other fishing gear, safety gear, etc.
WOT 42.5mph at 5000

To me the Saltwater Series prop is nearly ideal, it allows the engine to spin up to 5500 with a light load, when boat is loaded it still spins to 5000 (and it doesn't blow out).To be honest, I was amazed when we were able to get 49mph out of this setup.

Finally, the reason I post this is so others might find it helpful. I'm also reminded just how much weight affects twenty foot boats!

 

[onoahimahi]

Hi - good numbers, did you get a feel for whether there was a significant performance improvement that could be attributed to the motor height change alone?

 

[seasick]

I have recently read a member here was having troubles with his newly purchased boat (208 I think). We recently ran a few tests and I hope our results will help others.

2002 Grady 209 with every option available (T-top with curtains, freshwater shower, livewell, baitwell, leaning post, full cushions, etc), except raised bow rail. 2002 Yamaha 200 HPDI. Bottom paint in good condition. 2- group 27 batteries.

Test 1 13-3/4 x 19 Yamaha black stainless prop (original), engine mounted two holes up.
Boat loaded with sixty five gallons fuel, four people (800lbs), safety gear and minimal other stuff.
WOT - 43.5mph at 5300 rpm

Test 2 same setup as Test 1, but engine raised four holes (top hole)
Boat loaded with sixty gallons fuel, one person (200lb), safety gear and minimal other stuff.
WOT - 46.0 at 5400 rpm, boat steered a little better at cruise and prop still did not blow out

Test 3 15-1/2" x 19" Yamaha Saltwater Series II, engine on top hole
Boat almost empty, twenty gallons fuel, two people, safety gear, etc
WOT 49mph at 5600

Test 4 same Test 4, but full fuel (80 gallons), 800lbs people, 8 fishing poles, lots of tackle, food and drinks, other fishing gear, safety gear, etc.
WOT 42.5mph at 5000

To me the Saltwater Series prop is nearly ideal, it allows the engine to spin up to 5500 with a light load, when boat is loaded it still spins to 5000 (and it doesn't blow out).To be honest, I was amazed when we were able to get 49mph out of this setup.

Finally, the reason I post this is so others might find it helpful. I'm also reminded just how much weight affects twenty foot boats!

Very interesting results. Note that since most tests were with a fairly heavy load ( passengers and fuel) the boat sits lower in the water and on plane has more hull in contact with the water. Trim is critical and I assume that you adjusted motor trim to get the maximum speed for a given setup. Your performance at lighter loads will probably be different. Changing the motor mounting height has different outcomes depending on the thrust angle and that depends to an extent on how low the boat is sitting ( and that relates to load).

Test 4 was interesting in that your WOT revs were lower. That tells me that the prop diameter for that configuration was bit large. Of course at the same time, it would seem that the pitch was about right since there was not a lot of slip at the high end.

When you have nothing better to do, try a test with your passengers forward and then again with them sitting on the rear locker seats. Adjust trim as mentioned above and see how the change in weight distribution affect speed and revs.

And as you mentioned, these boats are relatively light and passenger load along with fuel weight can make a big difference in performance. The difference between half a tank and a full tank of gas is like carrying an extra 1 1/2 adults

Thanks for the report. I enjoyed it.