115hp EFi only 36 knots?

[Limecc]

Be sure to update us how you get on.

The only other way to pull that prop is to get a remap. JB Mechanical do outboards all the time, shame they are in Oz but they do postal return on your ecu.

[SARK]

Yeah I will do, hopefully in a week or so.
Never thought about tuning before, makes sense.

One thing haven't ever done, is trim up at max speed, outboard is generally level or slightly down in chop. Could there be a few knots in that?

Looking at props now, probably go for 17" 3 blade at the moment as Don't want too many variables

[Limecc]

Definitely you should trim up until it begins to ventilate then tilt down a bit.

Before spending any money on a prop you should always optimise the engine height and I think you've at least one hole you can go up. Doing that and getting the trim right should be the first thing.

You don't need an engine hoist, use the trailer jockey wheel method and the skeg takes the weight.

Buying from Steel Developments takes out the risk factor getting the prop choice slightly wrong.

[Limecc]

Originally Posted by SARK

Limecc
What's your thoughts on Orwell boy's Ribcraft getting 5300 on a 21p with 100hp

I had a look and Orwellboy's BF100 has a final drive ratio similar to Beerbelly's Command Thrust so it's normal for him to be able to pull a higher pitch than you even though slightly less power.

Top speed is comparable but I think it's overpropped. 1000 rpm down.

[Limecc]

Originally Posted by Limecc

Ribcraft recommend a 19p for 90hp in their brochure which is at odds with the stated performance of 34.8 knots at 6000 rpm. Must be a mistake, clearly incorrect as a 19p would give over 40 knots at that rpm.

Solved this mystery also. Their figures are correct. A DF90 final drive ratio is even greater so the prop is turning much slower than on a 2001 Mercury.

[Pipster100]

As Limecc says, you need to trim it up. Personally, before changing anything, I'd go out on a pretty flat day, hit WOT and trim up as suggested until you reach the point just before cavitation and then see what your WOT rpm is. You can make a judgment if you should lift your engine up 1 hole. If the cavitation plate is currently in line with the bottom of the hull you may find lifting up 1 hole doesn't give you the grip in the rough stuff.

On my Ribcraft 585 and Yam150 F, the cavitation plate is inline with the bottom of the hull. At WOT and trimmed down I'll hit 5400rpm, trimmed up I'll hit 5900rpm

[SARK]

Just spoken with a friend who had a newish 115hp on a 6.8M avon, he got 45 knots! I think a new engine though gives much better power.

I plan to be with the boat tomorrow, check the engine height, & hopefully take for a quick blast in Poole Harbour & try the trimming.

Thanks again for your input, much appreciated

[Limecc]

Originally Posted by SARK

Just spoken with a friend who had a newish 115hp on a 6.8M avon, he got 45 knots!

See if you can find out what prop and which engine. Sorry for being slightly skeptical at this stage.

[SARK]

Originally Posted by Limecc

See if you can find out what prop and which engine. Sorry for being slightly skeptical at this stage.

Hi five prop (can't remember pitch), 2014 yammy 4-stroke which was tuned

[Pipster100]

So your friends 2014 115 Yam you're comparing too has been tuned? To what? Also is it a shallow V Avon? I really think you're not to far off the mark with your engine. You're currently getting 36kts at 5000 rpm trimmed down. See what you get trimmed up.

As an example, family's A600 Ribeye with a Yam115 F (Circa 2008) trimmed up with 1 onboard will just hit 40kts at WOT, can't remember the exact rpm but pretty close to max 6000.

[Orwell boy]

Originally Posted by Limecc

I had a look and Orwellboy's BF100 has a final drive ratio similar to Beerbelly's Command Thrust so it's normal for him to be able to pull a higher pitch than you even though slightly less power.

Top speed is comparable but I think it's overpropped. 1000 rpm down.

I appreciate this help .thankyou ,your certainly got this subject sorted ,
rather funny even the honda selector doesnt seem to know the 100hp version exists

[SARK]

Originally Posted by Pipster100

So your friends 2014 115 Yam you're comparing too has been tuned? To what? Also is it a shallow V Avon? I really think you're not to far off the mark with your engine. You're currently getting 36kts at 5000 rpm trimmed down. See what you get trimmed up.

As an example, family's A600 Ribeye with a Yam115 F (Circa 2008) trimmed up with 1 onboard will just hit 40kts at WOT, can't remember the exact rpm but pretty close to max 6000.

Avon adventurer, just an example of what some 115hp can do.
Isn't the old 115hp a 1.8L, & newer ones are something like 2.1L? So probably producing & maintaining a full 115hp.

Good to know I'm not far off then
Hopefully I can get closer to my goal of 40 knots too.

Thanks 👍

[lakelandterrier]

TBH I'd be more concerned abut a comfortable and economic cruising speed/ set up then maxing out on speed alone.

How often will you be travelling WOT, and for how long?

Personally I'd want a set up that gives me a comfortable ride over a day out than a technical what is is possible to max absolute speed.

You and I may have different wants from our boats, so this is not a criticism, just a view.

I hope you manage to get the set up that delivers foe you.

LT

[SARK]

Originally Posted by lakelandterrier

TBH I'd be more concerned abut a comfortable and economic cruising speed/ set up then maxing out on speed alone.

How often will you be travelling WOT, and for how long?

Personally I'd want a set up that gives me a comfortable ride over a day out than a technical what is is possible to max absolute speed.

You and I may have different wants from our boats, so this is not a criticism, just a view.

I hope you manage to get the set up that delivers foe you.

LT

I feel like there's something not right, so if I'm under performing in wot, I'm probably under performing cruising too. Efficiency & power.

Like buying a range rover but it only does 90mph, even though you will mostly be doing 30-40mph, you still want it to perform how it should.

But yeah I know what you mean, just feel like I should be getting more from it

Thanks

[SARK]

So...
Cav plate is about 2 inches above bottom of transom.
Trim tap had quite an angle on it, now straightened.

As the weather is crap I knew I wouldn't get a proper test.
However I came across locally a great condition SS Mercury Vengeance 16" prop for £115, which I bought.
I've read some people experience SS add 200 revs as they don't flex compared to aluminium. So I figure it may be equivalent to a 17".
It wasn't, got 6100-6200 revs & 37 knots, experienced lots of cavitation too (due to 16" pitch?)

So 3" less pitch on SS got me 1200 extra revs.

I'll try my Ali 19" prop again when weather calmed down.
Otherwise potentially a SS 19" might rev better, instead of a 17" Ali prop.

[Limecc]

Originally Posted by SARK

So...
Cav plate is about 2 inches above bottom of transom.
Trim tap had quite an angle on it, now straightened.

As the weather is crap I knew I wouldn't get a proper test.
However I came across locally a great condition SS Mercury Vengeance 16" prop for £115, which I bought.
I've read some people experience SS add 200 revs as they don't flex compared to aluminium. So I figure it may be equivalent to a 17".
It wasn't, got 6100-6200 revs & 37 knots, experienced lots of cavitation too (due to 16" pitch?)

So 3" less pitch on SS got me 1200 extra revs.

I'll try my Ali 19" prop again when weather calmed down.
Otherwise potentially a SS 19" might rev better, instead of a 17" Ali prop.

2" is too high and the source of your ventilation. I thought you said the anti-cav plate was level did you adjust It? It works out at 3/4" per engine hole so you need to drop it at least one hole if not two.

The bargain 16" prop can be converted to a 17" pitch and then some more by adding a little cupping. Give Steel Developments a call.

A 19" stainless prop is taking you in the wrong direction.

I reckon it was a valuable exercise.

[johnrambo]

At 5000 rpm, 19 pitch, with a 2.07 gear ratio your max speed with 0 slip wold be 37.7 knots. You cannot physically go any faster then that without increasing rpm.

At 35 knots you would be experiencing 7% slip so you are probably right on the money.

[SARK]

I thought it was about level, or not too low at least. So definitely not drag slowing it down.

I never experienced cavitation with the 19" prop, with a smaller pitch does that increase the chance of cavitation? To which yeah I'll need to lower it.

If 1" of pitch is around 200 they say
Going stainless with 3" less, I gained 1200 revs, thats double at 400 per inch compared to aluminium. So would you not think a Stainless 19" might not give me a few hundred more? 5300-5400 revs probably still low once I'm loaded.

Converting the 16 is definitely an idea, price depending.

Thanks again

[SARK]

Originally Posted by johnrambo

At 5000 rpm, 19 pitch, with a 2.07 gear ratio your max speed with 0 slip wold be 37.7 knots. You cannot physically go any faster then that without increasing rpm.

At 35 knots you would be experiencing 7% slip so you are probably right on the money.

With a couple of extra people on board & more fuel, think it will bring me down a few hundred revs? So 17" better?

Any experience with Stainless getting more revs?

Thanks

[mikehhogg]

does the word economy come in to any of these equations, how many knots are enough,how fast is fast enough.