motor position

[mausili]

i have a 88 172 sportcraft fisherman with 1.6 seadrive. with the seadrive being so heavy and the engine that far back from transom should the ventilation plate be at bottom of boat or should it have been raised. also seems to me the motor trims to far in. should it trim in parellel with transom or perpendiclar with ground. my problem is when motor is trimmed all the way down on take off the motor wont turn rpms, but if i trim motor up let rpms build than lower motor boat plains before motor is all the way down.

 

[Texasmark]

Re: motor position

I never ran one but if the engine is loading up it has too much work to do for the available hp. When you let the engine rev then drop it in the water you already have your rpm's developed which means you already have your HP developed (HP= torque, rpms, a constant of proportionality) ....all you have to do is stick it in the water and use it. As I see it, to cure your problem you would need more HP or a lower pitched prop to lighten the load on the engine so that it could increase it's rpms under the load and start developing it's rated HP......butttt if your boat runs out like you want it as it is once on plane, leave it alone! Just figure it's the nature of the beast and it is.

Mark

 

[mausili]

Re: motor position

it has a 17p ss on it now and have tried alum 15p that came on it with no difference. i thaught the ss with the holes drilled in it would let it slip.

 

[Texasmark]

Re: motor position

it has a 17p ss on it now and have tried alum 15p that came on it with no difference. i thaught the ss with the holes drilled in it would let it slip.

That's what they are for but there is a limited contribution. Hole diameter determines amount of ventilation (slip). If you take the two limits you have no slip with no hole and so much slip that the boat doesn't even move with too large a hole. Adjusting the hole size allows for say a couple hundred rpm over normal in the hole which in addition the rpms come up much faster than normal and once on plane the prop locks up, holes are bypassed and engine loads up....rpm's drop back to where they would be at that mph with no holes.

I'm going to say that you are so over propped that you haven't gotten there yet with your propping. I can just guess from here, but I'd bet there is something to what I say.

Mark

 

[mausili]

Re: motor position

let me throw this in also. when boat is at rest in the water the water line at the stern is to my self bailing holes (which were lowered by a previous owner about a 1 1/2). now wwhen motor is trimmed all the way in my upper exhaust ports go under the water surface. to me when motor is trimmed in the bottom of motor is closer to transom than top. i also think with the weight of seadrive and lenght off the transom the ventilation plate could be higher than keel by a couple inches. i also forgot to mention i have smart tabs

 

[Texasmark]

Re: motor position

let me throw this in also. when boat is at rest in the water the water line at the stern is to my self bailing holes (which were lowered by a previous owner about a 1 1/2).

1.

now wwhen motor is trimmed all the way in my upper exhaust ports go under the water surface. to me when motor is trimmed in the bottom of motor is closer to transom than top.

2.

i also think with the weight of seadrive and lenght off the transom the ventilation plate could be higher than keel by a couple inches. i also forgot to mention i have smart tabs

3.

1. Don't see the relevance to anything here. A picture of your setup would really help me and anyone else interested in helping you.

2. The holes are exhaust relief holes and they are there to improve starting and idling to "unload" the engine of it's exhaust gasses that would otherwise have to push their way to the surface from the underwater exhaust which impedes starting and low speed performance. The comment about full trim may be as simple as moving your tilt pin out a notch or two. Once the trim pushes the engine against it, the overpressure relief on the trim unit will open and the trim will stop at the pin and relieve itself.

3. Both of those (tabs/vent plate location) would improve performance, not hinder it. A picture would help.

Mark

 

[mausili]

Re: motor position

View attachment 151079
this is all i have right now. i will have to jack trailer up to get motor down will dig in ground even with tongue all the way down.

 

[mausili]

Re: motor position

also water line is at self bailing holes. if u zoom in u can see a dark mark above bailing hole that is where they were. thats alot of boat in the water is it not

 

[Philster]

Re: motor position

Raise the engine. You have setback. Your prop is most likely too low (actually, its extremely likely). Every 10" of setback requires the prop to come up about 1-1.5".

It all makes sense. Your conditions scream -- and I mean scream -- Raise the engine!!. With the setback and the engine sitting on the far end of a lever, the prop is lower than it would be if it were on a shorter lever (no bracket). It's buried and smothered. Your symptoms are spot on for this being the issue. The pic nails it.

Raise that engine at least 1-1.5" and then it still might need to go higher after test runs. I am willing to bet you will need to go about 3 or more inches up. At some point, it will be too high.

 

[mausili]

Re: motor position

Since there is no room on transom to raise what do y'all think about making a "Jack plate type bracket where the grey meets the black and use a round pipe in the center of the two metal plates cut on an angle so I can get the bolts in. The only thing is I would have to get height pretty close unless I start with two inches and make motor side of plate tall enough I can drill a second set of holes.

 

[Texasmark]

Re: motor position

I don't have an OMC catalog for reference but Mercury runs 1300cc on their 90 triple and 1800 on their 100 hp. So, I'm guessing your engine is about 85 to 100 hp. The boat has a high degree of dead rise at the transom which makes for some really nice soft riding but it takes a lot of thrust to get it up and on plane. Looking at your prop it looks like you have a lot more pitch than the 17 you mentioned. Wouldn't doubt that in comparing apples and oranges you got the same results (17-15p performance). If you want a comparison you need the same prop with less pitch.

The comment about water and the holes in the spray rail makes sense as the dead rise is so high it puts the mounting position for the engine low. So, assuming you have a lot of weight back there in addition to your engine, I would say that's normal. One other thing is the "apparent" weight of your engine. When talking about torque wrenches for example there is a formula used and the measurement is foot-pounds. It means you can take a 10' pole with a 1lb weight on it or a 1' pole with a 10lb weight on it and produce the same twisting action (moment of inertia). Hanging your 350lb engine off the end of that bracket adds 2' to the apparent weight, the weight that the boat feels and that doubles your effective engine weight for boat balance, hence your transom sits lower in the water than normal and yes between that and the dead rise, the drain holes are at the water line.....all makes sense. Additionally, that is another reason that you are stern heavy when trying to get up on plane.

Why is your engine mounted on the bracket and not the transom anyway?

You don't have that large of an engine, the prop seems to have excessive pitch causing the engine to load up on hole shot and I totally agree with Philster that you need to get the engine up having it mounted back there as he said.

I think I'd take that bracket off and mount the engine on the transom like normal and you'd be a lot better off. Your apparent weight would be half and your trim tabs would be even with the engine and do a better job of lifting the transom during hole shot.

Mark

 

[mausili]

Re: motor position

I see what u r saying about the two different props that's all I had to go by. I replaced the original black motor that came on it and naught two identical motors hence the color difference the motor on the boat now came with that prop and says 17p on it. I will take picture for u to double check me. As far as mounting the boat is two pieces at rub rail that motor came on that bracket from sportcraft. Fabricating what I have is all I can unless taking the sea drive off mounting Armstrong and replacing mid section of motor with standard mounts

 

[Texasmark]

Re: motor position

I see what u r saying about the two different props that's all I had to go by. I replaced the original black motor that came on it and naught two identical motors hence the color difference the motor on the boat now came with that prop and says 17p on it. I will take picture for u to double check me. As far as mounting the boat is two pieces at rub rail that motor came on that bracket from sportcraft. Fabricating what I have is all I can unless taking the sea drive off mounting Armstrong and replacing mid section of motor with standard mounts

I don't understand what you mean about the mounts and two pieces on rub rail and all that.

An engine of that size would "hang" on the transom and be through bolted to the transom. When installed on the transom, even with your high dead rise at the transom deep V, the anti-vent plate would be above the lowest tip of the fiberglass when the engine was 90 degrees from a line you would draw down the side of the boat....i.e. theoretically, if the boat were sitting perfectly horizontal, with the engine perfectly vertical (90 degrees) the anti vent plate would be above the lowest part of the fiberglass that makes up the hull/transom.

I have been thinking about this all day and your solution is what I said. Get the engine off that bracket and mount it on the transom as I just described. Leave your tabs and for now, keep your 17P SS prop that you said was ported......for the record, a prop shop can open your ports to help your hole shot. Just experiment with expanding them till you get the desired effect. As I said earlier, open them up to get what you want but not so much as to over do it and do too much revving coming out of the hole....trial and error on this part.

Finally, you said something about replacing the original black motor and all that.....are you talking about props, or did you have another engine on the boat that was black and you replaced it with this 1.6L Sea Drive? Hopefully, you were addressing the two props!

Get busy, get the engine on the transom and get back with us. 3M makes some super marine sealers, 5200 or something like that that will seal the holes from the bracket and the new holes you drill to mount your engine......taking the bracket off will also help to reduce your transom weight and help to solve your problem.

I want you to get this fixed and share it with us.

Mark

Mark

 

[mausili]

Re: motor position

hopefully these pics will help. the midsection of this setup is different than a standard motor i can't hang it off the transom. as far as rub rail, from there up unscrews and the top of boat and floor seperate from hull its like 18" thick on top of the stern.

 

[Texasmark]

Re: motor position

hopefully these pics will help. the midsection of this setup is different than a standard motor i can't hang it off the transom. as far as rub rail, from there up unscrews and the top of boat and floor seperate from hull its like 18" thick on top of the stern. View attachment 151215View attachment 151220View attachment 151221View attachment 151222View attachment 151223

Got it. I see the pitch so, so much for that. I also see that you can't hang the engine off the transom, so much for that. I guess we are stuck with raising your engine. Your bracket doesn't seem to have a way to adjust it. CMC or something like that is an after market supplier and I have followed some threads on here where people use their jack plates. The JP is adjustable and you can jack it up as high as necessary to solve your problem. I think they are around a couple hundred bucks. They may sell them on here.

Like Philster said, you may need to get up 3" to get where you want to be. On the prop pitch, if it handles your boat well when up and running then just concentrate on the jack plate.

Mark

 

[Texasmark]

Re: motor position

Got it. I see the pitch so, so much for that. I also see that you can't hang the engine off the transom, so much for that. I guess we are stuck with raising your engine. Your bracket doesn't seem to have a way to adjust it. CMC or something like that is an after market supplier and I have followed some threads on here where people use their jack plates. The JP is adjustable and you can jack it up as high as necessary to solve your problem. I think they are around a couple hundred bucks. They may sell them on here.

Like Philster said, you may need to get up 3" to get where you want to be. On the prop pitch, if it handles your boat well when up and running then just concentrate on the jack plate.

Mark

I just www'd and found "CMC Jack Plates" easily; not sold on this site. They are 2 piece, easily adjustable with a wrench up to 5". Perfect.

This edit is the next morning from this original answer. Some bad news as I see it so far.

I stuck "1.6 Liter OMC Sea Drive" into my Google search engine and came up with some interesting replies. Before the site cops throw me in jail, I loaded the same question in this site and got nothing for an answer....lots of answers but none dealing with the subject....so in your grace, please forgive the following:

I played with some of the replies and picked up a few pointers but the real "meat" was at another site titled "thehulltruth"....leaving the prefex and suffix off and let you add it. There was a lot of pictures and a lot of jabber about them and numerous usage and changeover senario's . Suggest you go over there and get some ideas.

In short, I doubt the conventional jack plate will work for you. The Sea Drive is an integrated unit (to my learning) and doesn't look to be easily adaptable to a jack plate....but if you can figure out how to add it, I'd go for it.

One guy did draw a picture of what Philster said in his initial response to you that the engine is begging to be lifted. Looking at the cartoon the guy drew he showed how the water came up behind the boat and any engine placed back there (off the transom) had to be higher mounted or it would be too deep and offer poor performance....hence the "raise her up". He was talking about shallow water operation, but what we are talking about applies too.

Here's the kicker you won't like. Some of the boats that are laid out/configured/setup whatever, like yours in even 18' have a 2.5 liter sea drive not the 1.6 you have. That compares favorably to my estimation of your HP being around 85-100 hp and theirs 175-200. That goes along with what I said about in my opinion, with your rig and all the stuff at the transom, your engine is too small to fight the load of getting on plane. Granted those engines weigh 600# to your 300 or so, but they have the power to brute force their way through it.

I wish I could be of more help, but without being there and rubbing elbows with you to solve this this is about the best I can do.

Good Luck,

Mark

 

[mausili]

Re: motor position

I think I come up with something where the grey meets the black my only concern is the steering arm. The motor on there now had hydrolic and the original was mechanical so I made a new arm that I bolted to the ears. Anyway the bend in that arm is at least 2 inches so I could flip it the problem will come trying to get 3 inches. Yeah I have searched these motors and sportcraft boats would u believe they put thus same 1.6 on a couple of 23' cuddys. Thanks again for all your help mark. One more thing what do u think about motor angle when trimmed all the way down. Is it me or does it look to far in.

 

[mausili]

Re: motor position

Oh and horsepower is 115 according to their sales brochure and I think that's at flywheel not prop so really at 90-100 like u mentioned

 

[Texasmark]

Re: motor position

I think I come up with something where the grey meets the black my only concern is the steering arm. The motor on there now had hydrolic and the original was mechanical so I made a new arm that I bolted to the ears. Anyway the bend in that arm is at least 2 inches so I could flip it the problem will come trying to get 3 inches. Yeah I have searched these motors and sportcraft boats would u believe they put thus same 1.6 on a couple of 23' cuddys. Thanks again for all your help mark. One more thing what do u think about motor angle when trimmed all the way down. Is it me or does it look to far in.

On this rig I doubt that you could get too far in theoretically. What you want in hole shot is to get the boat on the water and the bow (front of the boat) down. Soooo you want it tucked in as far as you can get it....within some reason.....15 degrees from 90 degrees with the hull.

Problem is that when you trim all the way in you put max pressure on the engine and require the most HP out of it at that time and that is part of your problem. I think you are HP limited. You proved it to me when this thread first started. You said that if you trimmed out and came down with it you could get on plane before it got all the way down. I answered explaining how your engine HP was coming into play.

I Have one other solution and it will take a Laser II which is a Merc prop but the only difference is the number of splines on the prop shaft.... a prop shop could re-hub it for you. This prop has huge holes and offers plugs to reduce the hole size. You could start with no plugs and if you ventilated too much on hole shot....engine revs excessively and not much forward motion, then start plugging with large down to small plugs till you get what works.

That will/could work for you at minimum expense and trouble. Then once on plane, you could use the benefit of your 17P and go about your business. I just scanned this thread and nowhere did you tell me/us what your WOT speed (gps preferred) and rpm's were running your 17P ss prop. Before we leave this I would like to know that answer as that will determine what pitch Laser II you might choose to look for. So get back on here with the numbers and let me see them.

As far as water in your exhaust relief holes, either you are going to have to get some stern weight forward, or maybe start off with enough trim out position to get them up so that the engine can breathe. You are not going to/shouldn't hurt anything with power head with them being submerged when running other than putting excessive exhaust pressure on the engine which makes for poor starting/running.

One more thing I would like to know. Get your boat up and running at WOT and trim for the best performance in smooth water. Get back near the transom about half way between the side of the boat and the center and shoot a picture of the engine in the slipstream. I want to see how high the engine is in the water when you are running top out. That may help in considering if you are in all that bad a shape other than getting your hole shot with another prop. I'll check in on this and stay with you.

Mark

 

[mausili]

Re: motor position

I have gotten 38mph via GPS @ 5300 wot with me and wife in the boat. I have looked at stern when running but that was to see position of tabs which they are right above the water. I can trim the motor a great deal and through peak performance than no change for a bit until it starts to blow out and I will assume that is just before tilt kicks in. I need to see where vent plate is. Bad thing is we have another a weak of cappuccino weather here in St. Augustine.