Need advise on RPMs shooting up like 500RPMs w/ new engine

[the brain]

Need advise on RPMs shooting up like 500RPMs w/ new engine



This is a repower. Here’s the vessel at rest more on it lower down. cav plate is like 2" underwater remember this is a work in progress while being used Image image
vessel at rest.jpg

vessel at rest2.jpg

previous engine height.jpg

1st shakedown run seamed normal an yes I had it floored on all these runs, I usually don't cruise much it's WOT as much as possible except for speed zones video

https://www.youtube.com/shorts/ks2P76MutxY



2nd shakedown run wasn’t a run at all just cranked ideled then water alarm came on so I turned her off. There was a little water pump discharge seam like the weak stream I have w/ the garden hose in backyard. video.

https://youtube.com/shorts/OBEBKFpmw2A

3rd shakedown run seamed normal then RPM Shoot-up to 6K RPM but then lowered itself to normal 5500RPM video

https://youtube.com/shorts/mm99-VALy_U

4th shake run she shootup the RPMs

https://www.youtube.com/shorts/VoOHohqGcyo



5th Shakedown run seamed like things where improving a bit then the on oil alarm came on. I have a half filled oil reservoir.plan to keep fullish from now on.




6th shakedown run again RPM shotup to just under 6K so I pulled back on throttle then oil alarm again.

https://www.youtube.com/shorts/p55STnpueHY



7th run just putting over idel oil alarm again next crankup she was in limp mode won’t allow any increase in throttle. So limped back to dock.

https://youtube.com/shorts/p55STnpueHY



1977 24’ Starcraft Chieftain converted to outboard w/ armstronge bracket. Hull weight is around 1900LBs

Plus 2 batteries, 2 anchors,gear ect conservative estimated weight 2300LB plus 420LB engine so not real heavy for her size.



Same prop from previous engine 04 JohnsonBRP 175HP. Same engine height. previous engine height could be a tad lower All of these short runs where no trim up.
I think trim up will increase RPMs even more?
previous engine felt a tad stronger. But then again I haven’t been cruising for over 5 years so maybe I forgot how well previous preformed.

What I distinctively remember w/ PE she jumped up on plane instantly. but back in the good ole days I would go straight to WOT unlike in these initial shakedowns



The new 012 ETEC 175HP G1 only 170 hours seams to be running OK just feels a bit different. Maybe she needs a tune up.

What I did was motor to middle of lake then did the WOT runs to confirm I had the correct prop.I didn’t venture far from the dock.



Not sure what to think about he RPMs shootting upto 6K an some runs a tad under 6K another run shot up then normalized to the 5500RPM which I believe is the desired RPM.please advise.thanks

initialy I wanted to use the tripod that holds the camera so I could video the engine at idel an at top speed to verifiy the correct engine height but couldn't find the tripod so I'll order a new one an post up videos specifically of engine height

t

 

[messabout]

first impression looks like a twin hull boat. . The sudden jump in RPM suggests ventilation/cavitation. Twin hulls will create a wave system between the hulls. At some speeds the convergence of the waves can land at or near the prop which could cause loss of "prop traction".

 

[the brain]

this vessel is a monohull just a one piece type hull not a catamerang. thanks

 

[SolGato]

If your prop has a rubber hub, I would check to make sure it isn’t slipping.

 

[baeckmo]

Give us pictures of the transom and drive leg on the dry, showing trim tabs and bracket arrangement.

 

[fallguy]

To me, the hub is spinning out.

But the bigger problem is etec. Not especially known for trouble free.

 

[baeckmo]

To me, the hub is spinning out.......

Speculations, doesn't explain the temp alarms!

 

[the brain]

Thanks messabout,SolGato,baeckmo an fallguy for advise.


The prop used for these tests was newist not many hours at all maybe 50 mostly saltwater.I can’t confirm it has a rubber hub, there sale pitch mentions the hub is interchangeable so it’s probably rubber can I look at it while it’s assembled an see rubber?

I’ve never disassembled a hub so I don’t know.


IIRC it’s a Michigan wheel or could be a Solas both are inexpensive props. My plan back w/ previous engine was to narrow down the desired prop then step up to a stainless steel equivalent.


Here’s the engine height w/ straight edge under hull close to keel w/ engine turned straight forward.I say close to keel bc there is a chin right at middle of keel so straight edge is basicely on the hulls skin.

Which technically isn’t the lowest part of hull.

image


2 an 3 quarter inch below top of water inlet. This may explain the water alarm on only one of the shakedowns.

image

side view image

19” setback image

Rear view.

Engine is mounted at engines lowest point.

Engine is mounted at pods highest point I thought this would be a middle point allowing further adjustments if nessasary.

I have 1 ½” of downward an upward adjustment.


Edit: pod is 19” setback I used the rule of thumb 1” lower for every 12” setback.for Calculating the pods height mounted to transom. for engine to mount at it’s middle point for 1 ½ “ higher than the keel.


Edit2: all these shakedown runs where straight no turning an no trim up.
edit3: a high engine may explain why the ETEC didn't feel as powerfull as previous engine bc the prop isn't getting enough traction. (this as mention in orginal post).
Edit4: this prop isn’t in perfect condition it has a couple tiny dings still no vibrations. This 19 pitch is my lower pitched prop, I have 2 others both similar diameter another aluminum 21 pitch an a viper stainless steel 14.25x 22pitch both mite be to much RPM.but that’s another story.
from my research the ETECs is size HP likes preform better w/ a 14.25 diameter I believe bc of the velocity it spins.

Thanks for advising

 

[baeckmo]

No wonder you have both propeller and thermal issues, that's one of the worst arrangements I've seen for a long time! I'm surprised you move forward at all....! And forget about hub spinning, it's not the case; I think you have a Merc "FlowTorque" hub; it is not rubber and if it spins it is destroyed and does not grip "again". The problem is that you have installed the engine as if it had a large diameter surface-piercing propeller and separate cooling water intake. It has neither.

A/
At low speeds (before planing) you have water "rolling down" along the bracket bottom to the transom lower edge, bringing air bubbles from the surface down to mix with the water flowing aft along the boat bottom. That mixture goes directly into the cooling water inlets and accumulates in the water pump inlet, causing inception of cooling loss already at low speeds.

B/
At high planing speed, the flow from the keel region leaves the transom edge with a slight upward inclination; the water surface will meet the gearhousing forward edge slightly above the torpedo (height depending on speed). The shape of a standard Etec gearhouse is quite good, but it is NOT designed for this kind of surface piercing, so you will have occasional heavy spray diverting the flow from the propeller disc, and alas no cooling water at all and less water for the prop to work on.

C/
You have something looking like a transducer mounted to the transom a few inches to SB. That fellow will cause additional asymmetrical spray that disturbs the inflow to the prop.

I really don't see the logic in the application of a pod which sets the engine back without following up with a "flow-shaping surface" that defines the incoming surface to the screw. In your case your prop is expected to produce thrust from whatever comes into its working disc, be it water, air or stardust. The prop setback technique requires precise engineering and can be advantageous for high speeds in boats with well defined operating envelop, and where the prop is running in surface mode, but not for general boating.

In addition, what you have here is not a special issue for Etec engines, which has wrongly been suggested in a previous post!

Edit: Michigan props "Xchangeable Hub" is similar to the Mercury hubs; no rubber, but a urethane or equal plastic hub.

 

[fallguy]

Speculations, doesn't explain the temp alarms!

oil alarms, temp alarms, wild rpm jumps in milliseconds

probably more than one issue eh?

I only offered a simple check of the hub. It takes like 5-10 minutes.

After the pictures, lots of obvious.

 

[DogCavalry]

If you (quite rightly) want to use the etec, lower it so it can bite and get water, or use the HO leg with the extra ports in the torpedo for surface piercing, and get a big ss prop with heavy cup. Better to just lower the outboard. I bet it was a 25" leg on the Johnson, and the etec has a 20" leg.

 

[fallguy]

If you (quite rightly) want to use the etec, lower it so it can bite and get water, or use the HO leg with the extra ports in the torpedo for surface piercing, and get a big ss prop with heavy cup. Better to just lower the outboard. I bet it was a 25" leg on the Johnson, and the etec has a 20" leg.

Indeed odd how two engines could be so different.

 

[baeckmo]

Indeed odd how two engines could be so different.

What do you mean, there are four standard rig lengths; 15, 20, 25 and 30 inches, nothing odd there other than someone may have swapped a long for a shorter version. Note "may", since DC shooting a "betting" suggestion.

 

[philSweet]

I suspect your geometry is right at the hairy limit of shallow draft for that engine, and it looks like you have already run it through the mud. Prop damage is probably causing ventilation and rev rise, since you didn't have it at first. The cooling thing is a real problem, though. You may need an aftermarket remote pickup for it. It just depends whether you can live with another inch of motor depth.

Found this - WATER PICK-UP KIT, P/N 5006337, 5005124, 5005063 & 5007081 INSTALLATION INSTRUCTIONS | Crowley Marine https://www.crowleymarine.com/d/tech_article/water-pick-up-kit-pn-5006337-5005124-5005063--5007081-installation-instructions

 

[fallguy]

What do you mean, there are four standard rig lengths; 15, 20, 25 and 30 inches, nothing odd there other than someone may have swapped a long for a shorter version. Note "may", since DC shooting a "betting" suggestion.

I’m trying to be nice is all!

The single most important thing when buying an outboard other than hp is the length. I don’t need to tell you. So, I find it odd the OP would miss is all. But perhaps it could happen if it was swapped down below and the engine said something else, as you suggest.