Is this motor mounted too low?

[whistler]

Mercury 200EFI on a 23 Sceptre. Does this look like the motor is too low?



Picture was taken at cruise speed. I can't tell if I simply did not trim up enough or the motor is indeed too low. Performance is acceptable, but I feel it can be slightly better (2-3MPH). With a relatively light load (2 people, 3/4 tank), max speed is 40mph at around 5300 (need to double check). Prop is a Mercury Mirage Plus.

[DonV]

I think so! I had my 225 EFI on the next to last hole, you look to be on the top hole. I then went to a 6" manual jack plate and raised it even higher. In your pic you can not even see the AV plate! The good news is it's easy to raise.

[NoBones]

The plate should be between an inch above or below the bottom of the boat..
Put a straight edge with a jack to the bottom keel (IE: 2 X 4 etc.....)
long enough that you can have the plate level with the straight edge...
I run all my motors an inch above with no issues...

[flyingfrizzle]

Agreed, too low. I normally start with the av plate 1" above and move up from there depending on prop, use and normal running conditions. Long as your LU can pick up water it will be happy running high.

[whistler]

Thanks for the feedback gentlemen. I am chasing an unrelated intermittent problem with the motor and will lift the motor up one or even 2 holes as soon as its running 100%. I will report back with before and after performance numbers.

[flyingfrizzle]

Originally Posted by whistler

Thanks for the feedback gentlemen. I am chasing an unrelated intermittent problem with the motor and will lift the motor up one or even 2 holes as soon as its running 100%. I will report back with before and after performance numbers.

Don't be shy about your intermittent problem with your 2.5 merc. Me, bigshrimpin, nobones and others are fairly knowledgeable on those model outboards. May be able to help you solve your issue. The merc 200 2.5 is far my favorite outboard.

[whistler]

Gents, i recently raised the motor up 2 holes and the boat runs better! I saw about 43mph at WOT and holeshot is improved. I did not get a good picture of the cavitation plate but I think I can still come up one hole (to the highest hole).
However, the boat has become very prone to prop blow out in turns. At cruise (about 30mph) with the motor trimmed up fox maximum speed, even in very gentle turns, the prop blows out if I do not trim down ahead of time. Is this typical?

[FLexpat]

Originally Posted by whistler

Gents, i recently raised the motor up 2 holes and the boat runs better! I saw about 43mph at WOT and holeshot is improved. I did not get a good picture of the cavitation plate but I think I can still come up one hole (to the highest hole).
However, the boat has become very prone to prop blow out in turns. At cruise (about 30mph) with the motor trimmed up fox maximum speed, even in very gentle turns, the prop blows out if I do not trim down ahead of time. Is this typical?

Sounds like you are close to the right hole. After that is dialed, you should look at the prop next. You probably picked up a couple hundred RPMs at WOT going higher. I had a discussion with Ken at PropGods a while back about blowout on turns; if I recall correctly he said that could be fixed by adding more cup in the tips. I'm not a prop guru but the fact that you are having to trim way out to get the bow up makes me think you really need a bow lifting prop and don't have that now. Plus with the motor set right you may need a bit more pitch. Sceptres tend to be more bow heavy than CCs. Try a Merc Bravo I 4 blade prop if you can get you hands on one the right pitch. Optimizing motor position and prop combos for performance is a somewhat iterative process. Ken is a good resource and you may have a good prop shop nearby too - often they will let you try a couple to dial it in.

[whistler]

Thanks for the feedback. Sounds like I am getting closer to the correct motor height. Next time I am out, I will take a picture of the AV plate and make note of RPM at WOT.
I have seen several recommendations for a Mercury Revolution 4 prop. Anybody have experience with the Rev 4 on a 23 Sceptre? What about a Bravo 1?

[flyingfrizzle]

Once I got my secptre 20 up high to the best mounting point for performance I had some blow out in sharp turns as well with a 3 blade mercury vengeance prop. I went from it to a rev-4 and it got way better. The rev-4 is a simi-surface prop and it has the cup to handle the higher mounting height. You can go back down one hole too but then you will be giving up performance. The mercury mirage props have better cupping than most others also and would help if you wanted to stay 3 blade. Just remember a rev-4 19P will RPM like a 3 blade 17P, so if you go to the rev-4 you may want to run one-two pitch sizes up unless you need the extra RPMs to get you up towards your redline of the outboard.