Engine trials - we have the wrong prop

[webcraft]

Just fitted a Beta 16 on our Morgan Giles 30 to replace a dead Yanmar GM20

We kept the original prop. Today we recorded 2.3 knots at 600rpm, 6 knots at 2,000 rpm and a maximum rpm of a bit over 2,600 rpm (should be 3,600) where we were doing 7kts through the water. The morse control was all the way forward at this point, but I could not help noticing that there was at least an inch of lever movement from slow ahead until the revs started to increase.

Could there be an issue with the morse control, or does it suggest that the prop is oversized or over pitched.

Whjchever. I AMm delighted with 6kts at 2,000 rpm

BUT...

Is there an issue with only running at 60% of max rpm for extended periods of time? The engine seemed warm enough to me, though there is no temp gauge.

- W

 

[PetiteFleur]

Sounds like it's over propped - speak to a prop supplier who can advise the best prop for your engine and boat. I have a similar problem in that my Beta 25 on my 33' boat only revs to 3300 when it should go to 3600 rpm. Probably a reduction of 1/2" on the pitch should solve it but not got round to it yet...

 

[Boater Sam]

First check that the Morse is opening the throttle full at the engine lever.
No problem running at less than peak revs if you are happy with the speed.
I would get a temperature gauge fitted, its a necessary warning to save an engine in the event of water loss/blockage.

 

[stevie69p]

Just fitted a Beta 16 on our Morgan Giles 30 to replace a dead Yanmar GM20

We kept the original prop. Today we recorded 2.3 knots at 600rpm, 6 knots at 2,000 rpm and a maximum rpm of a bit over 2,600 rpm (should be 3,600) where we were doing 7kts through the water. The morse control was all the way forward at this point, but I could not help noticing that there was at least an inch of lever movement from slow ahead until the revs started to increase.

Could there be an issue with the morse control, or does it suggest that the prop is oversized or over pitched.

Whjchever. I AMm delighted with 6kts at 2,000 rpm

BUT...

Is there an issue with only running at 60% of max rpm for extended periods of time? The engine seemed warm enough to me, though there is no temp gauge.

- W

I have a Beta 20 on my 30 footer. It seems happiest around 2500 rpm, with a max of 3600. In flat water, at 2500 the boat is doing around 5.5 knots and at 3000 it's doing about 6.5.

I don't know whether your issue lies with the prop or not, but maybe the above figures will help in some way.

 

[webcraft]

If we can do 6kts at 2000rpm, is there a downside, because I am having difficulty seeing what it is.

- W

 

[webcraft]

First check that the Morse is opening the throttle full at the engine lever.

How do I do that? (Easily)?

- W

 

[stevie69p]

Any black smoke from the exhaust if you run it flat out in gear? Does it rev to maximum in neutral?

 

[RAI]

Have you looked at the colour of your exhaust smoke?
When mine was over-proped it built a nasty smoke stain around the stern.
I have a Max-prop, so reducing pitch is not a problem, though it took three goes to get it right.

 

[burgundyben]

It is important that you can reach max revs, you may find exhaust gas temperature higher than it should be if the engine cannot reach max revs.

Unable to meet max revs means that the propeller is demanding more power than the engine can provide.

A lightly loaded diesel is a happy diesel

Reduce the pitch.

Too much prop pitch is analogous to having 5 fat people in your car, a roof box and towing a caravan up an Alpine pass in top gear.

 

[scottie]

How do I do that? (Easily)?

- W

First Has anything been done to control during repair

Is it same engine and gearbox?

Disconnect the cable at engine end and check that you are getting correct travel

I suspect that the control has been set up with closed throttle in neutral but normally would be set with closed at first detent ie as soon as you move from ist detent revs increase

 

[Pye_End]

What prop are you swinging?

 

[TernVI]

If we can do 6kts at 2000rpm, is there a downside, because I am having difficulty seeing what it is.

- W

The down side is that your nominally 16HP engine will only be developing about 9HP max, maybe 10 at this RPM.
So, if you ever want to punch into some waves and weather, you will not have much thrust.
Check the morse cable.
Do a bollard pull test. What RPM do you get with the boat lashed to the pier?
If the engine reaches the same RPM lashed to the dock as it does at 6 knots, it's not (just) the wrong prop.

Do the maths and put the prop dimensions and gearbox ratios into one or two of the online calculators.
Put in the numbers for the old engine and see if they make sense.

 

[jwfrary]

Additional down side is over loaded engines produce extra soot, which jammed up the exhaust and will give you a nice stain on the transom. long term it will effect the longevity of the engine.

Simply check with the engine off that at the full throttle position on the more that the lever on the injection pump is resting on the max position screw. if not there's your issue. if it is, your overpropped as you deduce.

vic prop has a useful calculator which you can use to calculate the desired result.

 

[Amlov]

One of the problems with an over propped engine is that it can run a bit hot. The engine is having to work hard to spin the prop but the water pump impeller is not pumping as much water through as if the rpm was higher.

 

[Tranona]

Definitely over propped and will not do your new engine any good - in fact the Beta warranty would probably be void. If you have the standard 2:1 reduction the Beta recommended prop is 13*8 3 blade. Whoever sold you the engine (if it is new) should have advised what prop to fit. Your old Yanmar had in theory more power and a larger reduction ratio (so slower turning shaft)so you probably have a 14 or 15" prop.

You are missing a minimum of 800 rpm (you should be able to get within 200rpm of max). Rule of thumb is 1" of diameter or pitch alters revs by 250-300, so you need to lose between 2-3".
As suggested you can use Vicprop

Vicprop - Prop calculator for Displacement and semi-displacement hulls

if you have bought the engine secondhand or ask Beta. Make sure you get the reduction ratio right. It is either 2:1 or 2.6:1

 

[webcraft]

I suspect that the control has been set up with closed throttle in neutral but normally would be set with closed at first detent ie as soon as you move from ist detent revs increase

Not sure I understand. If this is the case how do I tell and how do I fix it?

- W

 

[Tranona]

Don't think that has anything to do with it. Your symptoms are classic overpropping. Correctly propped you would expect 6.2knots + at 3400-3600 and 5 knots at 2200. As I suggested earlier a prop for a 2GM is wrong size for a Beta 16!

 

[scottie]

I made a mistake in believing that you had repaired and not replaced the original engine so some my post is likely irrelevant

Check by disconnecting the throttle cable and see if you are getting full travel at the governor lever
So back to basics
You will have check and it’s easier without the engine running that the control is setup correctly

The gear selection is fairly simple when the control is moved does the selecter lever on the gear box travel correct
Because you do not want the engine revs to increase before the gear is engaged there is a lost motion device built in which is mostly a spring that absorbes the the initial movement so it is normal set up the throttle in the first detent ie in gear and then moving the control lever immediately starts to open the throttle
Travel measured on the cable is nominally 70 mm

It is possible that I am totally mistaken but the initial lack of revs along with not reaching expected Revs is a classic example of badly adjusted control
Sorry for messy post but it way past my bedtime

 

[webcraft]

OK, looked up the prop spec - it is 13 x 9.5

Should be 13 x 8

Is this massively over propped or just a bit?

Is it OK to rev the engine in neutral to see if it reaches maximum revs? This should determine if the throttle settings are a issue, should it not?

- W

 

[webcraft]

What prop are you swinging?

13 x 9.5

Should be 13 x 8

- W