Not reaching manufacturers WOT limits

[Caddwizard]

I don't believe I am reaching manufacturers WOT limits.

I own a 2004 Sea Ray 185 Sport specs are:
? Mercruiser 4.3 ltr TKS 190hp
? Gearing is 1.81
? Prop is 14.25 x 21 ( 832832A45P21)
? Hydrofoil attached

Maxs are:
? Idle speed is 650rpm
? WOT is 4100rpm
? Speed achieved on glassy flat water is 68km/h (42mph, 37kn)
? Based on full tank 98ltrs
? 2 adults and 2 kids + general goods and chattels (260kg)

Recently serviced with the same maxxed out results.

My figuring is that the prop is too big (too much prop as they say). I tend to go on long runs (ie not a lot of stop start towing) so am thinking of downsizing the prop to a 19 to up the revs and 4 blade for smoother running. Revolution 4 maybe?

If you have any suggestions based on similar boat conditions above it would be great to receive them. Not too sure if this affects suggestions but I am in Australia.

Thanks in advance

 

[tazrig]

Re: Not reaching manufacturers WOT limits

For every degree of pitch you decrease you gain about 150-200 rpm. before you go messing with the props, however... How long have you had the boat? did this problem just start or has it been going on for a while.

 

[Caddwizard]

Re: Not reaching manufacturers WOT limits

For every degree of pitch you decrease you gain about 200-300 rpm. before you go messing with the props, however... How long have you had the boat? did this problem just start or has it been going on for a while.

Have had the boat 4 months and have been out 9 times. Have had great fortune re water smoothness. Never been able to reach above 4100. I believe the motor to be sound.

 

[jestor68]

Re: Not reaching manufacturers WOT limits

For every degree of pitch you decrease you gain about 200-300 rpm. before you go messing with the props, however... How long have you had the boat? did this problem just start or has it been going on for a while.

That is 150-200 rpm per inch of pitch.

 

[jestor68]

Re: Not reaching manufacturers WOT limits

Based on your current performance, it looks mlike you might go to a 19 pitch prop.

 

[steelespike]

Re: Not reaching manufacturers WOT limits

The Hydrofoil could be lowering you rpm and speed.I would start by removing it.
Just off the top of my head I feel the 21 should get you into your rated rpm range.
Speed on glassy water could actually be slightly slower than water with ripples from a light breeze.
Is your speed by gps?Are you sure the throttle opens all the way?
Is the bottom clean and smooth?

 

[Bondo]

Re: Not reaching manufacturers WOT limits

The Hydrofoil could be lowering you rpm and speed.I would start by removing it.
Just off the top of my head I feel the 21 should get you into your rated rpm range.
Speed on glassy water could actually be slightly slower than water with ripples from a light breeze.
Is your speed by gps?Are you sure the throttle opens all the way?
Is the bottom clean and smooth?

Ayuh,... Welcome Aboard Caddwizard,... To add to SS's comments, 'n questions,...

Are ya trimmin' for best speeds,..??

 

[Mi duckdown]

Re: Not reaching manufacturers WOT limits

I would remove the hydrafoil and retest.

 

[Caddwizard]

Re: Not reaching manufacturers WOT limits

I would remove the hydrafoil and retest.

I will try with it removed. Your comment prompted some searching on that subject with mixed answers. Some said that it could cause cavitation.

Is there a way to tell your cavitating? I don't get any spikes in revs.

Thanks

 

[Caddwizard]

Re: Not reaching manufacturers WOT limits

Ayuh,... Welcome Aboard Caddwizard,... To add to SS's comments, 'n questions,...

Are ya trimmin' for best speeds,..??

Cheers

Thumb is sore from trimming (motor only) as I don't have trim tabs.

 

[Caddwizard]

Re: Not reaching manufacturers WOT limits

The Hydrofoil could be lowering you rpm and speed.I would start by removing it.
Just off the top of my head I feel the 21 should get you into your rated rpm range.
Speed on glassy water could actually be slightly slower than water with ripples from a light breeze.
Is your speed by gps?Are you sure the throttle opens all the way?
Is the bottom clean and smooth?

Have quoted GPS speed though the the boat reads the same. Have checked the GPS against 3 cars at the same speed and against other devices (time to kill on long trips to work).

Throttle is at full lock. You have made me think to see if I have cable slack or something preventing full stick so will check that out.

Many thanks

 

[reiddo1]

Re: Not reaching manufacturers WOT limits

For every degree of pitch you decrease you gain about 150-200 rpm. before you go messing with the props, however... How long have you had the boat? did this problem just start or has it been going on for a while.

I too would agree that for that horsepower and boat size, there may be other factors at work. It amazes me to see that the initial response from most when wot revs are not reached is to change prop configuration. Has the compression been checked on this engine? Has the fuel flow and timing been checked ? I know that the Caddwizard said the engine had been recently serviced but was the integrity of the engine checked. I just replaced a 200 hp Evinrude which was running at 4000 rpm at wot. Certainly not a prop problem. Number 5 cylinder had only 60 pounds compression at idle but on the starter motor it registered zero. Be careful before you spend a lot of money changing props prior to having a closer look at the engine.

 

[Caddwizard]

Re: Not reaching manufacturers WOT limits

It's been a while but thought I'd keep those who commented up to date.

Appears I had a faulty temp gauge. Was running much colder then thought which in turn was causing the choke to stay on.

Fixed the gauge and thermostat. Runs a lot smoother and getting WOT RPMs at 4400. Strangely no increase top in speed though.

 

[steelespike]

Re: Not reaching manufacturers WOT limits

Thanks for getting back your motor will be happier at a warmer temperature.
Did you try removing the foil?I think your motor should be at the redline and speeds in the high 40s.
I've seen 3.0s with a 21" prop run around 40.I've seen some claiming as much as 43 with the right prop.
Of course these 3.0s don't usually do well for water sports with that setup.