peterjaw
Well-Known Member
OK, I will follow your suggestions to turn off the ActivTrim and switch everything to "manual mode", and perform some experiments for acquiring some more experiences.
2 persons vs. 8 persons aboard
- Thread starter peterjaw
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OK, I will follow your suggestions to turn off the ActivTrim and switch everything to "manual mode", and perform some experiments for acquiring some more experiences.
BartW
Well-Known Member
this is with a outboard, so a petrol engine,
most on here have experience with diesel engines, that have constant torque at lower rpm,
in my experience with former petrol inboards, I also noticed a bigger influence from weight and trim positions, compared to diesel.
do you experience of lot of differece of getting on the plane with different load ?
the position of the people also makes a big difference (acording my former experience)
most on here have experience with diesel engines, that have constant torque at lower rpm,
in my experience with former petrol inboards, I also noticed a bigger influence from weight and trim positions, compared to diesel.
do you experience of lot of differece of getting on the plane with different load ?
the position of the people also makes a big difference (acording my former experience)
scottie
Well-Known Member
In the days when yachting was the pastime of Kings they often had very large crews and on the final leg of races when no longer required the crew were invited to step off the boat thus lighting it so perhaps you could try the same and discover at what point the weight ceased to affect the speed.
Ps they did change the rules to insist that you finished with the same number as you started
Ps they did change the rules to insist that you finished with the same number as you started
Rum_Pirate
Well-Known Member
Beamishken
Well-Known Member
You don't say what your rpms are doing flat out lightly loaded or when fully loaded. If your rpm is down on recommended rpm lightly loaded then it maybe you need to reduce pitch to allow the engine ro rev out more & therefore produce more hp to carry the load
Report back with rpm at wot with light load and heavy load
Report back with rpm at wot with light load and heavy load
Coustea1
Well-Known Member
I have a 350HP petrol engine (28ft boat). The drop in speed sounds like a lot. I took 8 people out only yesterday (so 9 on board in total) and lost about 1-2kts maximum. It is a bow rider so the weight distribution is probably better as I had 4 people up front. Leg was fully trimmed in, trim tabs fully up.
Rum_Pirate
Well-Known Member
The web site states:
10 passengers 400 hp and Maximum load (People, Gear, Engine) 1340 kg
A 300hp will weight in around 300kg.
So 8 people x 70kg = 560kg +300kg engine = 890kg + 80kg (8x10g gear) + 400kg (full fuel 400 L) = 1,340kg
So you are at the max load (for the 400hp max) BUT using an engine with 75% of max power.
Other factors:
What is the pitch of your prop?
What is the tachometer reading at (Wide Open Throttle) WOT with low load?
10 passengers 400 hp and Maximum load (People, Gear, Engine) 1340 kg
A 300hp will weight in around 300kg.
So 8 people x 70kg = 560kg +300kg engine = 890kg + 80kg (8x10g gear) + 400kg (full fuel 400 L) = 1,340kg
So you are at the max load (for the 400hp max) BUT using an engine with 75% of max power.
Other factors:
What is the pitch of your prop?
What is the tachometer reading at (Wide Open Throttle) WOT with low load?
peterjaw
Well-Known Member
Yes, I do feel a lot difference of getting on plane with different number of people aboard.
So, what did you do to improve? Moving your passengers as close to the bow as possible?
peterjaw
Well-Known Member
Hi Beamishken,
The RPM was about the same, lightly or heavily loaded. It's about 5500 ~ 5800 rpm at WOT.
peterjaw
Well-Known Member
Maybe I should ask my passengers to stay in the front cabin or close to the bow next time.
Thank you very much for sharing your experience.
peterjaw
Well-Known Member
My propeller is 15 x 14 SS Mercury Enertia.
The RPM is around 5800 at WOT with low load, and was 5500 ~ 5600 with 8 persons aboard.
Assassin
Well-Known Member
Actually they base it upon weight Martin, they assume 75Kg per male and use their own figures for children, more importantly is the need to read the specifications as they may state up to 4 adults with 6 children at a weight of """""""""".
BartW
Well-Known Member
putting more weight / people on the bow will improve getting on the plane,
but
this will dramatically reduce speed,
moving weight to the back will increase planing speed
when I was heavy loaded with one of my previous (petrol powered) boats, I asked two people to sit on the bow during acceleration,
and move to the back at planing speed..
AndieMac
Well-Known Member
I think you are on the right track RP, a single 300 HP outboard on a full size 28'er with a big/Max load is always going to struggle a bit.
They say HP sells the boat, but torque is what actually moves it.
Propping down a couple of inches will help get it up on the plane a little easier, but if it hasn't got the torque throughout the range to drive the extra weight, you won't get performance.
Beamishken
Well-Known Member
Seems odd to me that you loose so much speed but a minimal no of revs I think id be looking at a prop with larger diameter & or bigger blade area or maybe 4 blades.
peterjaw
Well-Known Member
So that means "tourque", right?
In fact, I don't have that much chance to take more than 3 persons, so I wonder if I should
replace my current prop.
gordmac
Well-Known Member
Could the prop be slipping a bit on the shaft under high load?
cstewart37
Active Member
Peter,
You NEED to look at the propeller that you have on the 300hp Verado !!! You are going to do damage to the engine if you are only getting 5500 WOT. You need to be aiming to be 6200rpm minimum. I have changed my Vensura 19” 4 blade for a 17” Rev4 & I am able to run at 6200/6400rpm WOT & I am getting better fuel economy with the same speed performance.
All the best CS.
You NEED to look at the propeller that you have on the 300hp Verado !!! You are going to do damage to the engine if you are only getting 5500 WOT. You need to be aiming to be 6200rpm minimum. I have changed my Vensura 19” 4 blade for a 17” Rev4 & I am able to run at 6200/6400rpm WOT & I am getting better fuel economy with the same speed performance.
All the best CS.
Bouba
Well-Known Member
That seems a bit high to me. I think 6000 is optimum. Have you got any spec that says 6200/6400 ?
