Engine Setup Enquiry - 370 Express, Dual 450hp XTO's

[Poz]

Hello all,
I have recently taken ownership of a 2023 370 Express with dual Yamaha 450hp XTO's.
The current engine setup on the vessel is with props of 16 5/8" x 19 and an engine mounting height, 3 holes from the top.

The current fuel figures, performance and range, I believe, to be not be as I would expect. After comparing figures from similar setups of other 370 Expresses, I am not getting similar results.

What I have struggled to find, is a solid description of the setup that these boats are running. If there is anyone who has a dual Yamaha 450/425 XTO on a 370 Express, are you able to offer information of your setup and performance figures, for me to compare.

Regards
RP

 

[seasick]

What performance data are you getting and what did you expect?
The mounting hole #3 is the recommended setting from Yamaha but the prop recommendations depends on what your priorities are.

 

[Fishtales]

I'd shoot a note to GW cust svc thru the website. They likely can provide some info.

 

[Poz]

What performance data are you getting and what did you expect?
The mounting hole #3 is the recommended setting from Yamaha but the prop recommendations depends on what your priorities are.

Hi, Seasick
Attached is the current performance figures that I am getting. The table is in metric units, as that's what we use here, sorry for any inconvenience. The first column is a test done on another 370 Express running dual 425 XTO's in New Zealand, in salt water, (this performance report, is on the Grady White website). The last two columns, are the figures that I have recorded from my boat. My test results, obviously also in salt water.

I am in Australia, and fish predominantly wide offshore and travel long distances to the grounds, hence why economy and range are the most important factors I am seeking.

I hope this provides the information you are looking for.

Regards
RP

 

[Poz]

I'd shoot a note to GW cust svc thru the website. They likely can provide some info.

Thank you, I am currently in this process through the dealer.

 

[seasick]

My initial calculations were so far off from what you would like to see that I questioned my methods.
I ran all the test data through two different prop calculators and got similar results.
The Grady 370 with 425s works out to about 10,5% slip
Your numbers ( which I find hard to be so far off from optimal) both work out to 30 something to 42% slip! Can that be correct? I have my doubts.
If so, the props are too small and probably need more pitch. Let's see what Grady says.

 

[Sauza45]

On the Grady website the 370 express comes with 3 450 xto's You said you have only 2 ?

 

[seasick]

On the Grady website the 370 express comes with 3 450 xto's You said you have only 2 ?

I saw the same thing but I looked further and twins or trips are options.

 

[drbatts]

Keep in mind that manufacturers published numbers are very optimistic and do not always mirror real world numbers. They are usually done in perfect conditions, without bottom paint and the boat is very lightly loaded.

 

[Poz]

On the Grady website the 370 express comes with 3 450 xto's You said you have only 2 ?

That Is correct, I only have two x 450 XTO's. There was an option to purchase triples or twins. I expected performance figures close to the review of the Grady 370 Express from New Zealand fitted with twin 425 XTO's on the Grady White web site.

 

[Poz]

My initial calculations were so far off from what you would like to see that I questioned my methods.
I ran all the test data through two different prop calculators and got similar results.
The Grady 370 with 425s works out to about 10,5% slip
Your numbers ( which I find hard to be so far off from optimal) both work out to 30 something to 42% slip! Can that be correct? I have my doubts.
If so, the props are too small and probably need more pitch. Let's see what Grady says.

Thanks Seasick,
So far the dealer has advised that Grady wanted to go down in pitch to 16 3/8" x 17. We have tested those props however the boat had only marginally better economy at cruise. WOT RPM went up from 5500 to 5800 but boat was more difficult to hold on the plane in heavier seas.
From your comments it may be worth testing the 16 3/8" x 21. I presume these props will increase speed throughout the rev range but possibly lower the WOT to 5100rpm. This would still be within the max rev range required from Yamaha. We tested the boat again yesterday with full fuel and 2 POB in calm conditions and could only get 4 bars of trim at 4500rpm before any further benefit in economy trimming out further. We could get 5 bars of trim at WOT (5500). The cav plates is sitting at approximately 3/4 inch above the bottom of the hull. Would there be an improvement in lowering the engines 1 hole. What are your thoughts?

RP

 

[Poz]

I saw the same thing but I looked further and twins or trips are options.

Correct, that was an option.

 

[seasick]

I am at a loss to explain the larger performance difference between your set up and the Grady published figures. The fuel consumption is 50% more and your cruising speed is down 40%.
I also don't fully understand what you mean by saying you were only able to get 4 bars of trim. Please explain what you are doing. I may have missed something.
I am surprised that Grady recommended going down in pitch

Are you sure your trim tabs are retracted for your tests? Play with them later.
If possible determine what trim setting corresponds to a vertical lower unit orientation and do your tests again

 

[Fishtales]

Keep in mind that manufacturers published numbers are very optimistic and do not always mirror real world numbers. They are usually done in perfect conditions, without bottom paint and the boat is very lightly loaded.

So true. Light fuel, no waste, water, gear, heavy people, ideal conditions (wind, current, tide etc), anchor/rode etc, Bottom paint is a big one especially with age (coats and conditions of hull),

 

[Poz]

I am at a loss to explain the larger performance difference between your set up and the Grady published figures. The fuel consumption is 50% more and your cruising speed is down 40%.
I also don't fully understand what you mean by saying you were only able to get 4 bars of trim. Please explain what you are doing. I may have missed something.
I am surprised that Grady recommended going down in pitch

Are you sure your trim tabs are retracted for your tests? Play with them later.
If possible determine what trim setting corresponds to a vertical lower unit orientation and do your tests again

Thanks Seasick,
Trim tabs are retracted for tests. 4 bars of trim is the blue bars showing on the Yamaha CL5 digital screen when trimming up. I am getting to 4 bars before ventilation noise.
I will check the vertical lower unit trim setting.
RP