Engine height question

[Fergus3060]

Evening all,

Ive recently completed a refurb (when is it ever actually complete) on an Artic 22 and I've fitted a Suzi 250 to her, currently running an 18" 4 blade prop. It's a bit small and reaches the Rev limiter fairly easily 2up (40kts), so looking to increase pitch 1 or 2". I'm also wondering if I ought to bring the engine up a hole. Currently it grips pretty well with the 4 blade.

Short clips at the links show where the anti vent plate is when running fully trimmed down at about 25kts. Grateful for thoughts.

https://youtu.be/r6BBeUGrrpw
https://youtu.be/SS3gSGSZrIY

It's also currently fairly flighty in the bow - a future mod will likely be an aux fuel tank up front, but in the meantime some ballast in the bow will have to do. But will raising the engine help with trim/attitude in flight? The links sort of show the attitude of the boat if only for a few seconds

https://youtu.be/hTr0jmDBoXs
https://youtu.be/K99neOSmwuw

[jonp]

Trial and error.

[Limecc]

Hi Fergus,

I haven't had chance to view YouTube yet but you should always optimise engine height if you've never done it before on your craft. Don't rely on whoever originally rigged it because they might have done so without sea trials.

It could earn you a free pitch or two of prop and also reduce torque roll (if that's a problem). Choice of prop, stern lift as opposed to bow lift may also help tame a flighty bow?

[Fergus3060]

Thanks Limecc. I sort of guessed at the height on the engine rigging based on some anecdotal info as I’ve taken her from double to single engine set up during the refurb.

Trial and error indeed. Not knowing what the end state should look like is my issue, so was hoping an experienced eye on the anti ventilation plate video might tell me if I’m about right. The answer may well be to hoik it up a hole and see if I get any negative effects.

The prop choice is the next question. I plan on doing some offshore passages so a bigger 4blade seems like a good choice for stern lift and grip, keeping the smaller for towing or as a spare etc.

[Limecc]

It's difficult to tell anything from your vids but I enjoyed them anyway. Nice boat.

So the way to go generally might be this approach: Starting with the AV plate one hole (3/4") up from level with the hull and with neutral trim, you shouldn't be getting any ventilation in a big sea. Obviously on a calm sea when you trim up, there's always a point at which it will let go. If the engine's too high you won't be able to trim up very much and raise the bow before that happens. It's all trial and error and how it feels. On mine I was able to go two holes up and now it's perfect which is just as well, I have no adjustment left.

I'm a four blade fan, but having said that I just purchased a Turning Point 3 blade which has a smaller diameter, higher rake and bigger pitch as an alternative to my Rubex C4. It's for when I'm alone in the boat and lightly loaded. Bow lift instead of stern lift, it should fly. But I mainly wanted to bring the rpm down around 25 knots cruising speed so I'm eager to see how it goes. TP have great reviews especially the four blade with dual geometry concept. I wont need to experiment with engine height like I did before.

[jonp]

Ive found 4 blade props have improved just about every boat Ive owned or skippered, extra cupping added might save you having to buy another prop.

[Limecc]

Originally Posted by jonp

Ive found 4 blade props have improved just about every boat Ive owned or skippered, extra cupping added might save you having to buy another prop.

New Turning Point prop was barely more money than having cupping added to my Solas.

[jonp]

Originally Posted by Limecc

New Turning Point prop was barely more money than having cupping added to my Solas.

I was surprised how good my 4 blade turning point was, it out performed several stainless 3 blade props of well known manufacturers.

[beamishken]

Easiest way to set height is jack it up one hole at a time until it ventilates excessively then drop it one hole & your about there. Cant tell much from a video over the stern tbh

Sent from my SM-G950F using RIB Net mobile app

[gtflash]

Agree. But also checking the AV plate is also a pretty good indication of reasonable water flow. I confirmed my height by running at fast speed. With fast trim. AV plate (the lower of the two) should be out of water but getting lightly splashed. I run water pressure gauge but never run out of cooling.

In practice it is tricky to witness AV plate. See my unsuccessful video. My camera man complained and I realised after, the trim tabs were causing a lot of the spray as we had a bit of a lean to correct.

https://youtu.be/UHvq6f1b2I0

Lifting engine will I increase revs so be prepared to hit rev limiter earlier. There’s several theory’s on adding an 2” pitch or so for 300-400rpm etc but it’s all trial. I run a 23 or 25 and both work but the 25 needs a gentle throttle to get up, but gives me more speed. 23. Is the everyday and I favour rev4s now as a do anything prop. It all depends what you want to do with the boat and how fast you want to go.