2 persons vs. 8 persons aboard

[peterjaw]

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.

Thank you very much for your advice, CS.

My current prop is 15 x 14 3 blade, what kind of prop will you suggest my to look at?

 

[Bouba]

Hi Bauba,
The spec is from engine's manual.

View attachment 79863

FYI!

Well, I take it back. It looks like Cstewart37 is right! It’s just that when I looked it up I found this,

 

[Bouba]

Ok, I’ve seen the discrepancy. On Peter’s specs it say 6 cylinder but on mine it says V8.
But you should follow the one that came with the engine! And everyone is right, the only way to increase rpm is to change the prop

 

[peterjaw]

Ok, I’ve seen the discrepancy. On Peter’s specs it say 6 cylinder but on mine it says V8.
But you should follow the one that came with the engine! And everyone is right, the only way to increase rpm is to change the prop

The one you found was for new Verado, 2019 version. Mine is V6.

On the other hand, to replace a prop is headache to me.
Do you think I should decrease the diameter with same pitch, or same diameter with lower pitch?

ps. I prefer opinions from here instead from Mercury local dealer.

 

[Beamishken]

The one you found was for new Verado, 2019 version. Mine is V6.

On the other hand, to replace a prop is headache to me.
Do you think I should decrease the diameter with same pitch, or same diameter with lower pitch?

ps. I prefer opinions from here instead from Mercury local dealer.

You wouldnt reduce diameter, if anything you should increase diameter or add blades or blade area to assist with the grip on the wzter but reduce pitch to allow the engine to rev out further

 

[Bouba]

Peter, you need to talk to your dealer to see if he has any spare propellers that you could try. They are expensive so you need to try as many as you can until you hit that magical 6200-6400 mark. I’ve done this before and when you do reach that 6400 your boat will perform better (but don’t go over 6400).
But usually the one recommended by the manufacturer will be the best, in my experience

 

[cstewart37]

Hi Peter,
The inline 6 Verado 300hp needs to be mounted high on the transom to get the best performance from it. It could be that your engine is mounted to low on the transom.

There is something seriously wrong with your setup as your performance figures are terrible!!! On my 7.5 mtr Parker with the 300hp l6 I can do 42kn at WOT 6200rpm & cruse at 4500rpm at 29kn & burning 45ltr an hour. Propeller is a Mercury Revolution 4 blade 17”. I would think your boat should only be about 10 or 15% lower figures than my setup.
Parker 75cc….. Weight without engine ca. 1.860 kg
Quicksilver Activ 855 Weekend …….Boat weight without engine 2713.00 kg (OB

If I was you I would be talking to the dealer that sold you the boat as there is something far from right with your setup big time !!!

From Powerboat & RIB test of 855 IB:
The VW 3.0 TDI V6 diesel engine that MerCruiser use here is a great motor. It punches out 320ft/lb of torque at just 1400rpm and a whopping 400ft/lb at 2250rpm. In boating terms, this translates to fast hole shot times. Given that it has a redline of 4200rpm and a pretty flat torque curve across the spectrum, this engine ‘should’ push the Activ 855 to over 30 knots.
I say ‘should’ because the best I got on the day was a two-way average of just over 26 knots, with what can only be described as lethargic acceleration. The boat’s new owner, who was on board for the test, told us he had been advised that it was a 34-knot boat, and seemed less concerned than me. The motor was only pulling 3900rpm and it took a bit of time to reach this engine speed. This suggests two possible problems: an overcoarse prop, or fouling around the sterndrive and/or aft section of the hull. I strongly suspect the latter, as the dealer that supplied this boat is unlikely to have made such an error in their propeller calculations. The fuel consumption figures were also not what I would expect of a frugal engine in a 3.6-tonne boat, so I suspect somewhere down this boat’s short timeline it has sported a small beard.

All the best CS

 

[Bouba]

Peter, you could start with a prop selector program like this
http://legacy.qsprops.com/prop-selector/#

 

[Beamishken]

Mercury have their own prop selector which may help you but no prop selector is 100%, they give you an idea but trial and error are the only 100% way to select the correct prop
http://www.mercurymarine.com/en-gb/europe/propellers/selector/

 

[peterjaw]

I have played with the prop selector and got this result:


My current prop is 14.5 x 15. It seems not very far away.

My question is: if I try the first 2 suggested prop ( 15 x 15 and 14.7 x 16), will there be noticeable improvement?

(Sorry if I just asked a stupid question.)

 

[Bouba]

I have played with the prop selector and got this result:
View attachment 79881

My current prop is 14.5 x 15. It seems not very far away.

My question is: if I try the first 2 suggested prop ( 15 x 15 and 14.7 x 16), will there be noticeable improvement?

(Sorry if I just asked a stupid question.)

It’s a good question!
Unfortunately I don’t know the answer. Somewhere in the island of Taiwan there will be a boat shop or outboard dealer who will have an old secondhand propeller that you can borrow (it’s been my experience that they use them for door stops ).
The alternative is to buy secondhand ones off eBay. Usually the aluminum props are much cheaper. But when you have found the perfect prop you will want stainless steel

 

[peterjaw]

It’s a good question!
Unfortunately I don’t know the answer. Somewhere in the island of Taiwan there will be a boat shop or outboard dealer who will have an old secondhand propeller that you can borrow (it’s been my experience that they use them for door stops ).
The alternative is to buy secondhand ones off eBay. Usually the aluminum props are much cheaper. But when you have found the perfect prop you will want stainless steel

OK, I will try to find someone who are willing to lend me various of props for testing.

By the way, I asked my engine dealer today why my engine can only reach around 5800 at WOT?

He said it's for protecting the engine. He said that in case the bad weather or bad driving behavier lift the prop out of water or near the surface of water, the rev could increase dramantically, even for a very short period, and the engine could be damaged.

So he did not push my engine to the maximum, just left some space for unexpected situations.

Well, I am not sure if he is right but sounds reasonable. Maybe this is so called "local wisdom".

 

[julians]

OK, I will try to find someone who are willing to lend me various of props for testing.

By the way, I asked my engine dealer today why my engine can only reach around 5800 at WOT?

He said it's for protecting the engine. He said that in case the bad weather or bad driving behavier lift the prop out of water or near the surface of water, the rev could increase dramantically, even for a very short period, and the engine could be damaged.

So he did not push my engine to the maximum, just left some space for unexpected situations.

Well, I am not sure if he is right but sounds reasonable. Maybe this is so called "local wisdom".

Your dealer is fobbing you off, the engine has a rev limiter to protect it in the situations you describe.

 

[Bouba]

Remember you only want maximum revs (6400) with a clean bottom. If you achieve it with slime then when you do clean your hull you will find you are under propped
Boats are a fun hobby

 

[Beamishken]

2 things in your last few posts surprise me, firstly that your dealer states he deliberately over propped your engine to protect it. That is garbage over propping an engine is more harmfull than underpropping and it can lead to burned valves or pistons in extreme circumstances a lightly loaded engine is far happier than an overloaded engine & wont come to any harm. Time to find another dealer I think!
The results from the prop calculator also surprise me, your current performance shows you are overpropped yet the prop calculator is saying you are underpropped you need the engine to rev harder a) because it will make max hp at max rpm & b)running loaded under rated max rpm can cause damage long term.
Hoe did you input the data into the prop selector? Iirc it gives 2 options you can input the boat weight hull style engine etc and it makes a suggestion or you can input your current prop ,wot rpm speed etc & it gives a result based on that information this is the option you need to use.

 

[peterjaw]

2 things in your last few posts surprise me, firstly that your dealer states he deliberately over propped your engine to protect it. That is garbage over propping an engine is more harmfull than underpropping and it can lead to burned valves or pistons in extreme circumstances a lightly loaded engine is far happier than an overloaded engine & wont come to any harm. Time to find another dealer I think!
The results from the prop calculator also surprise me, your current performance shows you are overpropped yet the prop calculator is saying you are underpropped you need the engine to rev harder a) because it will make max hp at max rpm & b)running loaded under rated max rpm can cause damage long term.
Hoe did you input the data into the prop selector? Iirc it gives 2 options you can input the boat weight hull style engine etc and it makes a suggestion or you can input your current prop ,wot rpm speed etc & it gives a result based on that information this is the option you need to use.

In fact, I did it twice. The first time, I entered the weight information and then
I entered current prop, wot rpm speed ... etc.

Both came out same (or quite similar) results.

Those information from local dealer are really confusing, that is why I am looking for all
advises from this forum.

Do you have any suggestion about how should I do with the prop?

 

[cstewart37]

Hi Peter,

There are two things you NEED to get right with the inline 6 Verado !!!

1 – Engine height on the transom the Verado inline 6 likes/must be mounted high on the transom.

2 – RPM at WOT needs to be as close to 6400 as possible – Most big HP Outboard engines run 4 blade propellers. I am very happy with my Rev 4 17" on the 300 Verado 6 inline.

As others has stated your dealer is clueless & has supplied the wrong propeller & there is a good chance that your engine is mounted too low on the transom.

All the best CS

 

[Beamishken]

Hi Peter,

There are two things you NEED to get right with the inline 6 Verado !!!

1 – Engine height on the transom the Verado inline 6 likes/must be mounted high on the transom.

2 – RPM at WOT needs to be as close to 6400 as possible – Most big HP Outboard engines run 4 blade propellers. I am very happy with my Rev 4 17" on the 300 Verado 6 inline.

As others has stated your dealer is clueless & has supplied the wrong propeller & there is a good chance that your engine is mounted too low on the transom.

All the best CS

Yep I'd pretty much agree with this if you have the oportunity to borrow some props I be trying to test 4 blade props and I wouldnt be surprised if your dealer has sat the engine right down on the transom. I'd be starting with the av plate 1"above the keel line and go from there

 

[cstewart37]

Hi Peter,

I have attached a picture of how my outboard is mounted as can see its mounted at the maximum height.

This would be the first thing you need to look at as you are running a 15” prop that should not be far away in size & if you have to lift engine you can then look at prop options.

All the best CS.

 

[peterjaw]

Hi Peter,

I have attached a picture of how my outboard is mounted as can see its mounted at the maximum height.

This would be the first thing you need to look at as you are running a 15” prop that should not be far away in size & if you have to lift engine you can then look at prop options.

All the best CS.

View attachment 79916

Thank you very much, CS.

As most advises here, I will check the mounting position first.

By they way, if you have chance, would you please take a photo when the engine is lowered?

I would like to see the distance from your prop to the transom bottom. Thank you very much.