Another engine height thread

[bleedblue94]

hi guys, working the details out of my build. had the boat out the other day but im fairly certain the motor is mounted too low so i took some pictures of it while underway at plane. i do notice the prop slips around 3500 rpm when i accelerate hard in a straight line, but im sure thats just a prop issue, and not a height issue. just want to get some advice before i lift it via the jackplate. also i do notice some slip (vent?) when i take a sharp turn at decent speed (yes i do trim down on turns). thanks in advance everyone.

 

[Bob_VT]

Re: Another engine height thread

Look through the other similar threads

Photos should be on dry land with the motor in a straight up and down position before you will get any guess to a correct answer.

 

[bleedblue94]

Re: Another engine height thread

I appreciate the response and I'm familiar with the traditional setting that you are talking about but that's not what I'm referring to. I have a jackplate and a few other factors that would make the motor drag if it were mounted w the cav plate even to the keel. Its well documented here and at prop gods that the proper adjustment is to be made based on observations while planing

http://www.veradoclub.com/smf/index.php?topic=137.0

 

[emoney]

Re: Another engine height thread

However, bleed, what Bob might be talking about is without seeing the LU of your boat it's hard to tell in the "on-plane" pics if it's right or not. Don't forget, you didn't even mention what the motor is.

If it's ventilating on turns, raising it won't help that....probably make it worse?

 

[bleedblue94]

Re: Another engine height thread

I apologize for that. Its an 83 175hp johnson 2 stroke

I'm not certain its venting. It may just be slipping in turns. The prop is a older 17 pitch aluminum that will need to be replaced but I want to get the height dialed in first and then decide on the replacement prop

 

[crb478]

Re: Another engine height thread

From your pictures your motor appears to be running to low. I can not see the av plate at all and there is a good amount of spray being thrown up

 

[Texasmark]

Re: Another engine height thread

I'm going to disagree with others on this being your best picture. After all, this is where the action is and looking at it on the trailer is good and I recommend it also, but this is where it matters.

I'm going to say that you could come up a notch or even two. I don't see the AV plate but from the pic, you aren't too bad. On ventilating, a cupped prop will certainly help if you want to run high in the water. Other thing is the hull configuration. If you have "disturbances" in the hull preceding the engine, in turns these will cause bubbles which will cause the prop to slip and rpms to increase. The only cupped alum. prop I am aware of is the Turning Point Hustler. Otherwise get yourself a SS..

I run my AV plate 1.5" above my hull and it is alum with a piece of 1" angle running right down the center of the hull where the two halves are welded together....bad news for high transom mountings and high speed tight turns normally.

Well it's not. I run a Ballistic SS prop with all the goodies of consumer grade high perf props and I don't have a problem. Actually, I will slow a bit as I go into the turn, leaving my trim where it was (all the way up) and about half way through I firewall it and it holds just fine. Lots of fun. Prop means a lot. On the trim being all the way up, my boat has a high angle transom such that I can trim all the way up in a straightaway at WOT and not blow out....but not far from it. On a shallower pitched transom pitch can't be raised all the way for the reason mentioned. My last boat was like that.

My 2c.
Mark

 

[emoney]

Re: Another engine height thread

I think the good news is you've got that adjustable jack plate so modifying the height should be pretty simple, right? If it were me, I'd start by raising it about an inch and then run it to get a true feel. Set-up is truly only verified "on the water". We can offer suggestions, but "proof is in the pudding", so-to-speak. I agree both crb & Texas in thinking it's a smidge too low and if I was a gambler (which I'm too poor to be) my wager would be on it being 1.5" to 2" too low.

If, by chance, that's a 25" motor, however, that changes it all. At that point, she'd be waayyyy too low, because if I'm not mistaken there'd be a 5" extension piece under water in your pics.

 

[Texasmark]

Re: Another engine height thread

If, by chance, that's a 25" motor, however, that changes it all. At that point, she'd be waayyyy too low, because if I'm not mistaken there'd be a 5" extension piece under water in your pics.

Agree.

 

[Sea Rider]

Re: Another engine height thread

Pics are not that sharp clear, but seems definitely your engine sits too high. Ideal height would be : with boat well ballanced towards bow, well trimed, at full plane at wot and AC plate riding paralell to water level, water flow should pass slightly under small upper water deflector plate. If using a 25" leg extension and happens to have a edge, water flow must pass under upper small plate. Same principles works same for short or long shaft motors sitting on short, long height transoms.

We been rigging mostly sibs/ribs with different engine brands, as we want to stay simple, none of them have electric trim, once set at correct trim (usually 2-3 hole out) stays there forever, just a matter to ballance well boat, have not had a single issue with prop cavitating at very close dime turns whatsoever once correct leg height is reached. And this test must be done under trial & error.

Make different engine heights test on flat calm waters, have a spotter check water flow progress and stay there once the sweet height spot is achieved. http://www.youtube.com/watch?v=oBeZjaA76VM&feature=youtu.be

Happy Boating

 

[Texasmark]

Re: Another engine height thread

Pics are not that sharp clear, but seems definitely your engine sits too high. Ideal height would be : with boat well ballanced, well trimed, at full plane at wot and AC plate riding paralell to water level, water flow should pass slightly under small upper water deflector plate. If using a 25" leg extension and happens to have a edge, water flow must pass under upper small plate. Same principles works same for short or long shaft motosr sitting on short, long height transoms.

We been rigging mostly sibs/ribs with different engine brands, as we want to stay simple, none of them have electric trim, once set at correct trim (usually 2-3 hole out) stays there forever, just a matter to ballance well boat, have not had a single issue with prop cavitating at very close dime turns whatsoever once correct leg height is reached. And this test must be done under trial & error.

Make different engine heights test on flat calm waters, have a spotter check water flow progress and stay there once the sweet height spot is achieved. http://www.youtube.com/watch?v=oBeZjaA76VM&feature=youtu.be

Happy Boating

I am assuming you rig for open water and not necessarily highest mph....since in open water, rarely do you get an opportunity to firewall it.

Under that condition I will agree that the engine needs to be lower in the water to prevent ventilation in swells. I was talking about calm water high performance where the drag of the lower unit is a big factor in getting all the mph you can get from your rig.

Mark

 

[bleedblue94]

Re: Another engine height thread

Sorry guys, I didn't see all the replies. Let me clarify.

Boat is primarily used on the finger and great lakes.

Boat requires a 25" leg

Motor is a 25" leg without an extention plate.


I'm fairly certain its too low according to the information put forth by prop gods whish see like a trusted source even here. The motor should not be even w the bottom of the boat bc of the 10" setback achieved w the jackplate. I know it has to be above the bottom of the boat, and I'm just looking for feedback. I have raised it 1/2-3/4" and will hopefully have it out for a test run this weekend.

 

[Texasmark]

Re: Another engine height thread

Sorry guys, I didn't see all the replies. Let me clarify.

Boat is primarily used on the finger and great lakes.

Boat requires a 25" leg

Motor is a 25" leg without an extention plate.


I'm fairly certain its too low according to the information put forth by prop gods whish see like a trusted source even here. The motor should not be even w the bottom of the boat bc of the 10" setback achieved w the jackplate. I know it has to be above the bottom of the boat, and I'm just looking for feedback. I have raised it 1/2-3/4" and will hopefully have it out for a test run this weekend.

I am going to go with Sea Rider on this........nuf said.

Mark

 

[Sea Rider]

Re: Another engine height thread

I am assuming you rig for open water and not necessarily highest mph....since in open water, rarely do you get an opportunity to firewall it.

Under that condition I will agree that the engine needs to be lower in the water to prevent ventilation in swells. I was talking about calm water high performance where the drag of the lower unit is a big factor in getting all the mph you can get from your rig.

Mark

In my particular case water flow keeps passing slightly under small upper plate once at plane or at wot, no difference at all. Works perfect on flat calm and choppy seas as well, by shimming height properly engine has gained 200 + revs than before, just need to throttle to 3/4 for best hole shot and back down to 1/2 throttle to maintain full plane and that's only a 18HP 2 stroke engine mounted on a 420 rib made to handle a 40 HP engine. Check avatar, only going at 3/4 throttle. Personally would play first with different engine transom heights, once set for best tail water performance, go for a wot spin, check max rpm achieved and play with props, pitches, etc, whatever suits your boating needs best.

Happy Boating