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Mounting Yamaha 70-Or Trying To
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| wpruitt |
Posted on 02/19/11 - 6:26 AM
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Putting a Yamaha 70 on a 15 Sport CC and the mounting choices are top bolt with blind plug, third hole from top by drilling bracket below blind plug or acquire a jack plate. I know the top bolt puts the motor too low and concerned the third puts it too high but would rather avoid the jack plate if possible. Opinions appreciated.
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| Phil T |
Posted on 02/19/11 - 6:48 AM
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Take a look at this article:
http://www.whalercentral.com/articles...icle_id=82
1992 Outrage 17 I
2019 E-TEC 90, Viper 17 2+
2018 Load Rite Elite 18280096VT |
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| wpruitt |
Posted on 02/19/11 - 8:09 AM
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Thanks Phil. Lag bolts may be my best, most flexible option.
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| Tom W Clark |
Posted on 02/19/11 - 8:19 AM
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NO, No, no.
You do not need to use lag bolts.
You do not need to use a jackplate.
You merely fill the two lower "blind holes" and drill two new one to allow the motor to be set one, two or three "holes up". The motor should NOT be set all the way down on the transom.
Please study the article Phil has pointed out.
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| wpruitt |
Posted on 02/19/11 - 6:34 PM
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Looks too close to the bottom of the splash well for me. If the drill was perfectly square to the transom it would be close. I don't trust myself to be that perfect with a hand drill. The bolts would also have to be inserted from the rear with nuts in the splash well which is not a problem but it is that close.
I have pulled the motor back off, and in process of filling the old lower holes. I have the yamaha bracket drawn in cad from their rigging guide. I will plot at full size and match from both sides to see how it fits before using the lags.
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| Tom W Clark |
Posted on 02/19/11 - 6:44 PM
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Looks too close to the bottom of the splash well for me.
Why?
If the lower bolt holes are only 6-1/2" below the upper bolts holes, they will clear by a mile. The motor will "two holes up" and you will still have the option of raising it yet another set of bolt holes.
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| wpruitt |
Posted on 02/19/11 - 7:32 PM
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Tom,
There is a 6.5" gap between the third hole down and the top of the slotted track. There is 7.25 inches between the second hole and the top of the slotted track. From the second hole there is 1/4" clearance to the splash well from a 1/2" bolt shaft. You are right if I knew I was going to use only the third hole down it will fit fine. The third hole puts the cavitation plate 2" above the bottom of the hull. The water intake is right at the bottom of the hull. Looks to me that the second hole is the most conservative location and best trade off.
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| Tom W Clark |
Posted on 02/19/11 - 8:08 PM
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Yes, your measuring is all correct.
If you only want the motor to be "one hole up" then drill the holes with a 7-1/4" vertical spacing and cut a flat on the washers for the lower mounting bolts, per Boston Whaler rigging advice (c. 1984)
If you want to use a modern stainless steel propeller, then use the third top hole for a "two holes up" mounting position.
This will allow you to drill the lower holes and use a full washer and it will also result in less lower unit drag, less steering torque, less bow rise upon acceleration and better top speed and fuel economy.
Having the cavitation plate sited 2" above the keel does NOT mean that it will be 2" above the surface of the water. This is an important, and all too commonly misunderstood point. The surface of the water will "rise" (as viewed from the boat) as soon as it comes out from under the hull.
The cavitation plate should never being dragging through the water while the boat is planing; it only aids the boat and motor while climbing on plane. "Two holes up" will be fine.
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| wpruitt |
Posted on 02/20/11 - 8:32 AM
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Thanks Tom! Great advice!
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| zotcha |
Posted on 02/21/11 - 6:27 AM
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Just out of curiosity Tom, for $225 Bob's Machine manual jack plate, do you feel there are any drawbacks to a plate?
I not only respect your opinion but appreciate your knowledge, willingness to assist, ability to explain on all levels, AND selling me the RIGHT prop at a price I could not beat. Thank you for all you do, here and on other sites, as well.
zotcha
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| Tom W Clark |
Posted on 02/21/11 - 7:35 AM
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There are advantages and disadvantages, costs and benefits of anything.
In this situation where wpruitt is just trying to mount his Yamaha 70, a $225 Bob's Machine manual jack plate represents an extra $200 he doesn't need to spend. That is almost enough to pay for a new stainless steel propeller.
I you want to use a jack plate to milk a little more top speed out of your boat, or minimize its draft, that is fine. But to spend hundreds of dollars on a jackplate simply to get an unattractive bolt hole adapter is silly.
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| surfncnow |
Posted on 02/21/11 - 8:20 AM
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I'm in the same position as the OP. I just mounted my 2 Stroke Yamaha 70 using the 3rd hole down (in other words, "two holes up"). My cavitation plate is about level with the bottom of the boat. Measuring from the top bolts down 6-1/2" I should have room for the lower bolts. My bolt washers will need to be bent to accommodate the curvature of the hull.
I tend to agree with Tom on the Jack plate. Jack plates serve a good purpose if you are fishing the flats or shallow water most of the time.
Edited by Tom W Clark on 02/21/11 - 8:33 AM |
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| Tom W Clark |
Posted on 02/21/11 - 8:38 AM
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The third hole puts the cavitation plate 2" above the bottom of the hull.
I just mounted my 2 Stroke Yamaha 70 using the 3rd hole down (in other words, "two holes up"). My cavitation plate is about level with the bottom of the boat.
Fellas, we have a very large discrepancy between those two descriptions. Where is the cavitation plate (A/V plate) relative to the keel?
wpruitt -- Are you sure you are not confusing the spray shield with the cavitation plate?
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| wpruitt |
Posted on 02/21/11 - 11:06 AM
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May be confusing the two. When I said cav plate I was meaning the larger horizontal structure on which the trim tab is mounted.
I, perhaps wrongly, measured the height above the extension of the line of the keel. I have no doubt you are correct on the proper mounting height.
I have to replace the prop as it has a 15p now and have a line on a 13.25x17 stilleto. I don't care much about top end but want good all around ability including pulling a skier. I am most concerned about over-revving with the 17p prop and so a 19 may be better as long as it pulls well.
Edited by wpruitt on 02/21/11 - 11:37 AM |
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| surfncnow |
Posted on 02/21/11 - 7:50 PM
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Tom W Clark wrote:
The third hole puts the cavitation plate 2" above the bottom of the hull.
I just mounted my 2 Stroke Yamaha 70 using the 3rd hole down (in other words, "two holes up"  . My cavitation plate is about level with the bottom of the boat.
Fellas, we have a very large discrepancy between those two descriptions. Where is the cavitation plate (A/V plate) relative to the keel?
wpruitt -- Are you sure you are not confusing the spray shield with the cavitation plate?
yes, that is correct. 2 holes up on the top set of holes. If I use a straight edge. My plate is a half inch higher than the keel.
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| wpruitt |
Posted on 02/21/11 - 8:32 PM
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Surfncnow,
Are you talking an older 15'? I pulled the engine to plug the blind holes and I measure 16" from the second hole up to the cav plate on the engine and 17.5" from the bottom of the keel to the top mounting holes on the transom. So the cav plate would be about 1.5" above the bottom of the keel on mine. I had eyeballed it before and measured 2" above the keel but that could have been off a bit.
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| Tom W Clark |
Posted on 02/21/11 - 10:56 PM
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The height of the transom, or any point on it, is measured vertically, not along the sloped angle of the transom.
It is the difference between the length of a triangle's altitude and it's hypotenuse.
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| wpruitt |
Posted on 02/22/11 - 3:52 AM
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I love it when you talk like that.
That would put my eyeball measurement about right then as it would be around 2" above rather than the 1.5". I will mount it higher to start...lot easier to change down than to change up.
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| Tom W Clark |
Posted on 02/22/11 - 6:39 AM
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I measure 16" from the second hole up to the cav plate on the engine and 17.5" from the bottom of the keel to the top mounting holes on the transom. So the cav plate would be about 1.5" above the bottom of the keel on mine.
No, not quite. If you measure 17-1/2" along the transom, then the top hole is about 16-3/4" *above* the bottom of the keel. That would place the cavitation plate about 3/4" above the bottom of the keel, much closer to what Surfncnow reports, and that 1/4" discrepancy may be explained by whether the measurements were taken to the edge of the 1/2" diameter bolt holes or to their centers.
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| wpruitt |
Posted on 02/25/11 - 3:22 PM
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Thanks to all. SurfNC was right. Two holes up or 3 holes down the cav plate is 1/2" above the keel. Looks good there. Thanks
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