Engine too low??? or am I obsessed?

[MTBfish]

OK guys, I have had great info exchange here, so here I go with more questions.    
Reference data.....  215 explorer 2002.   Running 200 Yama Saltwater series 320 hrs.

After getting here all set up for my Baja run, I am extreemly happy with how she ran and handled the ocean, had a few windy days, some good swell and chop and only picked up a few sparys when turning into the wind at slow trolling speeds...  

My issues continues to be the RPM range on the boat... after getting better at adjusting the trim I was able to get 4200 RPM once... but that is still way to slow for this motors recommended 5500 MAX.   if I can get up to or close to 5200 Id be much happier, and think the boat/motor will run much better.  

In looking at how the motor sits while plaining, it appears the cavitatiopn plate is running 2 or 3 inches below the surface, and additionally the plate seems to run non perpendicular to the surface of the water, its running at an angle.   The angel seems to be lower at the from of the motor and highr at the back, with almost 1 to 2 inches diffence betweein the front of the shaft and the back of the shaft.  this is where the boat seesm to cut the waves best, not porpuseing (SP?), and achive the best RPM after a long steady run.    

All this leads me to think that I need to get the motor higher on the tranasom to get the cavitation plate to run on the surface of the water while plaining...(and maybe it will corrrct the downward push the motor seems to be doing by running at an angle).  My options are drill new holes in the transom to achive this (i'm not keen on this at all) or add a Jackplate to be able to adjust the hight.
Edited... My motor is already on the highest hole posible, so I need to drill new holes or add a devise (jackplate ???) so I can raise motor higher...

Does this sound correct?   Do I sound obsesed with these thoughts about getting the correct hieght?   this set up is from the factory, so is my boat "off" in some way?   Anyone running a jackplate or similar devise to compensate?   Does anyone care?

Once I get over the engine hieght obsession, I will look at the prop options to do the final adjustments, but from what I have read, the drag the shaft and motor are adding, that is the 1st issue to adress defore looking at the prop...  Please help me decide on the correct approach.

Thanks and all oppinions welcome, as you can see I am confused and undecided... sorry spelling sucks and no spell check here....

Marc.  Happy Hoildays   :rendeer:

[slvrlng]

Yes its too low. Skoot has an excellent thread on here about his tribulations with his height on his hull. Actually the plate you describe is called the anti-ventilation plate. The main thing is 2 stroke love wide open and have a tendency to load the plugs and just not run as well if they can't get up to full song. Pics will help us help you more of course. So post some and lets see what ya got.
Here is a link to skoots thread hope this helps!

 viewtopic.php?f=5&t=5684

[flounderpounder225]

Marc,
Just some thoughts here.  #1 look closely at the transom bracket, the holes are very close together, and I have seen where they were covered up by too much silicone and sealant, I actually had a hole on one when I thought I was out of holes?  Just a thought.  #2 check the model number and take a measurement, and make sure the engine is a 25" shaft, and not a 30".  Your hull should accept the 25" motor without the anti-vent plate running under water.  How about a level angle photo of the stern of the boat floating a straight edge from the keel to the anti-vent plate with the engine trimmed down.  It might give you a better place to start because you can see it out of the water and visually see how much you are off approximately.

Marc (the other "C")

[saltfly]

Your motor is sitting to low on your transom. I agree with fp225. Check your motor from the underside of the mounting bracket to the top of your anti-ventilation plate. It should be close to your transom height 25 to 27“. Also you really need to see were your anti. plate is compared to the bottom of your hull. But even if you get it up. I fell because of how low your rpms are. You are going to have to change your prop. Your really loading that motor down. With  your rpms being that low. 2 stroke engines, like to run in their recommend rpm range.

[wingtime]

Marc,  Maybe I missed it but what size prop are you running?  I would say a 17" or 18" pitch would be about right for your boat.   Get a long straight edge such as a level or even a 2 x 4 and put in along the bottom of your hull extending towards your lower unit.  You should be an inch or two below your anti- ventilation plate.

[MTBfish]

Thanks for the advise, I will get some pics soon, and see about posting them... probably not in the water as I have just gotten all the salt off and covered her a while, don't want to do that again soon.

I appreiciate every who has read and responded so far, but please keep the info coming..

As for changing the prop I don't disagree at all, a new prop is in the future, but deciding the best stab at size and pitch  will come after I feel the motor high is been addressed to the best of my knowldge/or financial resouces.   The current prop is a 15 1/4 X 19 SS (guessing Stock prop).  M19 if I recall correctly.

Also forgot to metion, I did raise the motor up one hole allready.  I have another hole I could go up, but the bracket has 4 drilled holes on the top, and a long slot adjustement on the bottom.   The existing bolt on the bottom slot is very close to maxed out, so  can not raise the engine enough to keep that slot bolt in place and use the last hole on the bracket.   This is real hard without Pics... sorry.

Marc, the other marc, not to offend the Original,  FP225

[Aswaff400]

like everyone else said, anti-vent plate should be level, to 1 inch out of the water...

here a pic of mine cruising 4000 rpms, 40 mph, level trim...


you can see the plate for the most part is out of the water. when running wide open, the plate is about 1-1/2 to 2 inches out of the water. with a straight-edge on my keel, the keel is level with the top hole on the water intake. thats with the OB mounted on the 2nd highest hole...

[GoneFission]

That's a 'Rude picture!      

See ya on the water!

[flounderpounder225]

Thanks for the advise, I will get some pics soon, and see about posting them... probably not in the water as I have just gotten all the salt off and covered her a while, don't want to do that again soon.

I appreiciate every who has read and responded so far, but please keep the info coming..

As for changing the prop I don't disagree at all, a new prop is in the future, but deciding the best stab at size and pitch  will come after I feel the motor high is been addressed to the best of my knowldge/or financial resouces.   The current prop is a 15 1/4 X 19 SS (guessing Stock prop).  M19 if I recall correctly.

Also forgot to metion, I did raise the motor up one hole allready.  I have another hole I could go up, but the bracket has 4 drilled holes on the top, and a long slot adjustement on the bottom.   The existing bolt on the bottom slot is very close to maxed out, so  can not raise the engine enough to keep that slot bolt in place and use the last hole on the bracket.   This is real hard without Pics... sorry.

Marc, the other marc, not to offend the Original,  FP225

Marc,
Absolutely correct, you will probably have to do some prop work, but first and foremost your motor height has to be correct, nothing can compensate for that.  We have a lot of prop data on here, including my personal trials and tribulations with it, and we will have some solid input for that.
Marc

[fitz73222]

I could see raising the engine to gain maybe 200-300 rpm but not 1000-1200 rpm. What is your speed at 4200 rpm's? Are you sure your tachometer is working correctly? Are you sure of the propeller pitch? Something is not right here. Basically do a calculation of crankshaft rpm's divided by gear ratio = net propeller rpm X pitch minus 10% for average slippage = net inches per minute divided by 12 = feet per minute X 60 divided by 5280 to get miles per hour.

Here is my 60 bigfoot Merc on the flats boat speed calculation.
5500 rpm (WOT) divided by 2 (2:1) gear ratio = 2750 propeller rpm X 15" pitch = 41250 inches per minute minus 10% average slippage = 37125 inches per minute divided by 12 = 3093.75 feet per minute X 60 minutes = 185625 feet per hour divided by 5280 (1mile) = 35.15 mph. This is confirmed by GPS.
Your rpm's seem way to low even if the engine is down an inch or two.

See if your numbers jive with this calculaton method.

[MTBfish]

Raining like hell in Arizone yesterday, did not want to get all wet dealing with the measuring and picture taking in the rain.

Aswaff, appreciate the picture, but honestly, i don't see any plate anywhere, i'll take your word, but I cant see anything above the spray.  

Fitz, repeating, I don't think all my RPM issues are hight related, and I don't expect 1000 RPMs out of getting the hieght right, but 2 or 3 hun sounds like great results, that I can improve on latter with the prop changes.

I like the math approach, so here is what I got by following your calculation.
4200=2100 RPMS, (do all gearboxes do a 2/1 ratio?)  I assumed it was 1/1, but what do I know...


=(((2100*19)*0.9)/12*60)/5280

It gave me a Speed of 34.   Here is the problem, I think the GPS was reading in the 40 MPH ballpark...  

I remember 40 miles an hour at 4200 RP which does not math out, guess im i for another trial run.. bummer  

Keeping a 10% slip, I can make the math work if my engine is really turning 5K instead of 4200...

How can I confirm the Tach is working right?   It's the Yamaha gages, where I have 2 multi funtion gages that show everything...  The tach seems to have a nice constant ready, no eradich movement or jumping, zeros out when the engine is off and reads around 700 or 800 at idle.

[wpt03osprey]

I will be going through this exercise in he spring, My Yamaha 250 HPDI is sitting up 1 1/2 on the transom and I want to make sure it is correct.

I wouldn't mind a lower top end speed (never get to open up anyways)
 if I got a quicker plane without using tabs

[Capt. Bob]

Aswaff, appreciate the picture, but honestly, i don't see any plate anywhere, i'll take your word, but I cant see anything above the spray.  

Can you see me now

[flounderpounder225]

We have the same hull and same engine, I think my engine is sitting exactly where you described, if you are saying the transom bracket which holds the steering tube is about 1-1/2" over the top of the transom.  I moved it up one notch from where it was to get the anti-vent plate right at WOT and cruise.  All the props I tried during my experimentation had cavitation and slip coming out of the hole, and at about 20 Mph felt like it second gear, which was the prop completely "grabbing".  Then I tried and eventually bought the Mercury ENERTIA 15 X 15 from Ken at propgods down in S. FL.  He sent me the prop for free, and let me try it.  WOW!! Absolutely ZERO cavitation or slip coming out of the hole, almost impossible to blow it out in a turn, unless I am trimmed way up, it was the prop made for this big boat.  And that's exactly what Ken said they were made for, big heavy boats with large engines, the prop dwarfs a similar 15 X 15 I had, simply because the Rake of the blades is so big, it gives the prop a lot more surface area.  Once you get your height checked underway, I highly recommend the ENERTIA prop.
Marc  

I will be going through this exercise in he spring, My Yamaha 250 HPDI is sitting up 1 1/2 on the transom and I want to make sure it is correct.

I wouldn't mind a lower top end speed (never get to open up anyways)
 if I got a quicker plane without using tabs

[fitz73222]

Sounds like good advice to me! To answer your question; most outboards have a 1.87.1 to 2.3.1 gear ratio. The 1 to 1 gear ratios are for circle track formula 1 race outboards that turn low pitch cleaver style propellers at 9000-10000 rpms for acceleration. As for tach verification you can either borrow a known good tach and temporarily wire it in with your present tach tapping into the purple, gray and black leads or borrow an inductive shop tach from a local dealer to check calibration. Based on flounderpounders recommendation, 4" of pitch change from your current 19"; at an average of 250 rpms per inch of change is going to get you in the 5200 rpm sweet spot with a hole bunch of hole shot and load carrying ability. I`m not familiar with this prop design but 15" of diameter is a lot of bite!