How to check your OB motor height & wear the right prop!

[Megabyte]

I did my prop first, then raised the motor.
Prop helped greatly, raising the motor even more.

Photos below tell the tale.
Prop is a 17p Merc Mirage Plus.

In the photo of the motor you can see it was factory rigged as low as it could go.
As you can see, I raised it 2 holes but if I get the chance, it will be raised one more hole (all the way up).

 

[otolith]

Thanks Megabyte &shawnee83.

I'm going to run the boat and be sure where the cav plate is. I'll get some pics.

I'm sort of old school in so much as I think the way the boat is loaded has more impact than people realize. This is something I'm working on as much as I can. IMHO if the entire load is in the rear of the boat, everything will sit lower than it should. In a perfect world, the boat should be loaded so the boat is perfectly trimmed while sitting still in the water. Unfortunately this is seldom if ever possible.

I didn't really get an answer to the question, "shouldn't I be adjusting OB height and prop with the boat as it is most often weighted"? What is the logic of making these adjustments if the boat is seldom going to be weighted and balanced as it was during adjusting? For some reason, the questions seems sarcastic to me and this is not my intent.

 

[Megabyte]

I didn't really get an answer to the question, "shouldn't I be adjusting OB height and prop with the boat as it is most often weighted"?

In a perfect world, yes, but this is an imperfect world and your boat will almost never be static. It is a dynamic thing.

For instance... this summer I had 4 guests on board for a total of 6 people.
Full fuel, full coolers, and all of my gear plus the people.

It was a nice day so three of the four guest were sitting on the transom while the other two were sitting in deck chairs.
I was driving and I have to tell you, I could not trim the boat without moving some of those people forward and around the deck.

Once I got the weight distributed, everything was fine... but until I did, I was fighting it way too much.

Do the best you can for how you typically run your boat and you should be OK.

 

[shawnee83]

Permatrim just arrived. I'll post my results. Unfortunately, it looks like I won't be able to get to my boat to do the install until the weekend of 10-3. I will first have the motor raised to the top hole and then water test and document results. Second step will be to haul out, install the Permatrim, retest and document. I have pretty much made my mind up already however that I'm going to also install the 12x18" tabs probably over the winter/spring. I just don't see a down side to doing it, other than $. :lol: I'll keep updating as I progress thru the steps.

 

[otolith]

shawnee83

I'm curious how you determined what size tab is best for your boat?

I've seen some comments like "the biggest is the best" but that's crazy. There's some huge tabs out there.

Also, at what point does drag from tabs consume more efficiency than it provides?

 

[shawnee83]

shawnee83

I'm curious how you determined what size tab is best for your boat?

I've seen some comments like "the biggest is the best" but that's crazy. There's some huge tabs out there.

Also, at what point does drag from tabs consume more efficiency than it provides?

I guess I've based this decision on what other on this site gave done on their 2120's with the heavier F200 & F225's and my own evaluations from running my boat. My own personal experience with my 2120 has revealed that it has a pretty serious porpoising issue. Others with this engine combo and even some with the 150's have also mentioned it as well. That is probably the main thing that I'm trying to improve. The motor hight is just a piece of the pie but based on the information I've been given, feel it needs to be done regardless for optimum performance. As for the tabs (12x18" only), others here seem to have well documented that it has improved the porpoising on the 2120's along with planing time, slow speed planning and responsiveness. It can also be done without changing the actuators or their mounting position so that makes it a fairly simple fix. That said, I wouldn't put anything bigger on it as I don't think that would be warranted. Dale has mentioned several times that longer tabs rob fuel but wider ones don't or something like that. So you are correct about bigger can cause drag and increase fuel burn. I'm just a hack and riding on the coat tails of the guys who I think know about this stuff. Dale suggested the 18" tabs early on to me so I'm taking a leap of faith as I think he has had a lot of experience with this subject along with the others here and their results. The Permatrim is for the same reason as the tabs. The way I see it, the tabs won't hurt it and I can always remove the Permatrim if it doesn't work out. Crossing my fingers.

 

[shawnee83]

Sitting at docks in Beaufort tonight and wanted to post my initial and very limited results from the engine raising and Permatrim installation. I just didn't have time to do the raise and test then the Permatrim instal and test option separately as planned. I had my engine raised and then I went to my yard and installed the Permatrim. I barley had enough time before dark to run a quick on plane test. So far , the bottom line is that all of the important things have improved. Planing time, porpoising, low speed planing etc. No tabs and I could hold a steady plane at 3600 rpm and 19 mph. Bow angle better, no wake speed at 1100 to 1600 rpm I noticed much better straight tracking without near as much wandering. I raised to the top hole and I think that it could actually go higher to match what I've seen in the photos that were on Dale's link. I had less than a half tank of fuel and just my brother on board too, so not one of my heavier runs. Bottom line so far, if you have a F200 or F225 on a 2120, just go ahead and raise the motor to the top hole and call it done. Tomorrow is supposed to blow hard so maybe Sunday I'll have a chance to do some more runs and get better pics of the cavitation plate and RMP/speed/fuel burn data.

 

[shawnee83]

Update day 2. Light fuel of 1/4 tank or so and just myself on board. 3500 rpm, slight leveling tab for port down and maintained plane at 17 mph. WOT against current 6000 and 40 mph, with current 44.6. Raising the engine and instalig the Permatrim has improved the ride and general performance in just about every way. The big surprise has been improvement in the wandering at slow speed. She tracks nice and straight without constant steering input. On to installing the 12 x 18" tabs probably in the spring. If you have a 2120 with the F200 or F225, I highly recommend trying this set up. It may also work just as well with the F150's but I just don't know how the lighter weight would change the engine hight setting etc. I hope this helps. Feel free to PM me if you have questions.

 

[shawnee83]

One more from this evening. I was able to take a photo myself while my son drove the boat. 5500 RPM and around 40mph. You can see the shadow of the Permatrim a little better in this one. Still a little under the water but as Grouperjim mentioned, a tad on the lower side may have its advantages. Anyway, it's as high as it can go and I'm happy with it. I definitely need to trim down some and feather power for a reasonably hard turn, but that is as it should be. Calling this phase done.

 

[Megabyte]

Nice work.
Congratulations. 8)

 

[shawnee83]

Thanks Kevin. 12 x 18 tabs in the spring then maybe a prop. Tabs for sure though. I'll post results as I go.

 

[otolith]

This has been a great thread. I'm anxious to get my 2300CC back down to Mexico and in the water. I'm going to have to get someone to run the boat while I climb back there on the Armstrong to see where I'm at. I think I'll pre-rig a harness for myself.

 

[Megabyte]

I think I'll pre-rig a harness for myself.

Good plan!

 

[shawnee83]

Some data points to go with the changes.

 

[Daydreamer]

Sorry to dig up an old thread but this was so on topic to my question that I thought I would just add it to the information listed. I purchased a new 2510 XLD with and F300. I moved up from a 2310 with a F250. The 2510 is a much larger boat and is considerable slower out of the hole which is fine with me but my concern is that I can only turn 5400 RPM's and the Yamaha site says 6000 is the top end. Also, when I am running under 5000 RPM I get spray from under the motor near the prop that sprays up on the cowling. Not a ton hits the cowling but its a lot of spray when you are running at 4200 or 20 mph. it goes away at 5000 rpm with the motor trimmed up 4 bars. Its not the spray from the bracket that I used to get at slow speeds on the 2310.

at 4900 rpm I am going about 28 mph and burning about 1.5 or 1.6 MPG. Do you think this is dialed in right? I could not find a Yamaha bulletin on this boat with this motor. I am assuming it is similar to the 2520 performance but I could not find that either. My top speed is 33-35

 

[Megabyte]

Sounds like your motor is way too deep.
Can you post a photo showing what hole your motor is rigged at?

 

[Daydreamer]

I will get it when I am at the marina next. That is what the dealer was thinking as well but he did not suggest that it should be moved.

 

[Megabyte]

Mine was as deep as it could be and I experienced the same thing you are seeing.
I raised mine 2 holes and honestly, I should have raised it all the way up.
Even raising it 2 holes improved it immensely.

 

[Daydreamer]

Thanks for the reply Kevin. I ran the boat over the last few days and the motor is on the top hole which would put the motor at its deepest setting in the water. If you wanted to put the motor deeper in the water you could not because it is all the way down on the bracket.

Do you think raising the motor in the water would help more the searching for a new prop?

Tom

 

[Lucky John]

Sorry to dig up an old thread but this was so on topic to my question that I thought I would just add it to the information listed. I purchased a new 2510 XLD with and F300. I moved up from a 2310 with a F250. The 2510 is a much larger boat and is considerable slower out of the hole which is fine with me but my concern is that I can only turn 5400 RPM's and the Yamaha site says 6000 is the top end. Also, when I am running under 5000 RPM I get spray from under the motor near the prop that sprays up on the cowling. Not a ton hits the cowling but its a lot of spray when you are running at 4200 or 20 mph. it goes away at 5000 rpm with the motor trimmed up 4 bars. Its not the spray from the bracket that I used to get at slow speeds on the 2310.

at 4900 rpm I am going about 28 mph and burning about 1.5 or 1.6 MPG. Do you think this is dialed in right? I could not find a Yamaha bulletin on this boat with this motor. I am assuming it is similar to the 2520 performance but I could not find that either. My top speed is 33-35

On my canyon trips that's about all I have been avg............about 1.6 however I get 28-30 mph at 4300. WOT with less than a half tank I was pushing 5700. I know we spoke in pm, I was also considering going to a 4 blade prop but going to wait and see.
One thing I know is that this boat doesn't like to be run at just above planning speed 36-3900 it feels like it is laboring. I also have to stay aware that she likes her nose down which I accomplish with my trim tabs. A couple more trips and I will decide how to improve mileage.