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Jack plate question for a 17' Montauk
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| bottomfish |
Posted on 09/10/09 - 10:14 PM
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Well it is getting close to the time to re-hang my 2001 Honda 90 back on the boat. During the redo I filled the improper mounting holes (was mounted only using the top 4 holes) to start with a clean transom for the reinstall. I have searched the site and read all the arguements and have come to 2 choices and 1 other I saw today. I am looking for experience and or opinions on these.
#1 mount the motor a minimum of 1 hole up and try to squeeze the lower mounting bolts into the splashwell with plates or washers cut close to the botttom of the well. (worried about 2 holes up being to high)
#2 use a jack plate. Need to consider the added weight and possible performance issues.
#3 cut a round hole in the vertical wall in front of the splashwell above the rigging tube and dig the foam out back to the tramsom and throughbolt it as meant to be. This allows for adjustment up or down. Cap hole with round gasketed deck plate. (Saw this done on a 1960's 17' at the boat shop today)
I would like to make sure I can mount a different motor in the future if needed. I have had multiple bracket mounted outboards but all on much larger boats. Performance was great but just not sure yet.
Only want to do this one time. Thanks, Wayne
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| joninnj |
Posted on 09/11/09 - 4:02 AM
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Hi Wayne,
I am in the same boat as you (pardon the pun... The issue I also see is finding one that will clear the drains in the well without notching out the jack plate or making significant modifications. As far as weight I do not think they weigh more than 10 or 12 lbs.
My 17 has a Yamaha 90 mounted flush on the transom, I know it can be raised but I would need to drill new holes at the bottom of the well and do not want to do that. Would rather drill in to the jack plate if need be.
Also In the future if I change the engine no issues with mounting. Right now I am leaning toward Bob Machine Shop Convertible 4 inch set back, but have not confirmed that it will clear the drains. This model allows for multiple configurations. If I do not have enough steering cable it can be adjusted to a 2/12 setback instead of 4...
As far as performance I am sure there will be an improvement. My last boat was a 20 ft Hydrostream with V6 merc, I saw very big improvement which allowed me to use better a prop design to run closer to the surface and not break loose of the water,
Any Ideas on Jack plates for a 17 hull, Please???
Edited by joninnj on 09/11/09 - 4:03 AM
Jon in NJ
Many other boats and outboards in my boating history
The Whaler is the one I like the best!!! |
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| Tom W Clark |
Posted on 09/11/09 - 7:44 AM
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As of now you have a clean slate to work with. The top two holes are on layout and you've filled the lower two holes. There is no reason in the world not to do it right and drill the two bottom holes on layout but raised at least 3/4".
This will allow you to mount your Honda and any other outboard in the future using the standard BIA bolt holes.
There are absolutely no motors ever made that need to mounted all the way down on this hull. Regardless of what motor you own, you would ALWAYS start at least "one hole up" when mounting it.
In the case of the Honda BF90, you would do better to mount it two holes up.
Be sure to review this article for details:
http://whalercentral.com/articles.php...icle_id=82
I would not use a jackplate in this situation for several reasons.
The Honda 90 is a heavy motor. Moving it backwards will only shift the center of gravity of the boat further sternward and aggravate the stern heavy balance.
The jackplate itself will add cost at this point. You save nothing,money or labor, by using one.
It will also add a little weight itself, something you do not want to do.
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| bottomfish |
Posted on 09/11/09 - 8:08 AM
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Tom, I filled all the holes due to the top holes were down 2 1/4 O/C from the top of the transom. So I am truly working with a clean slate. My main delima is the worry of mounting two holes up. If I do so I can hit the splashwell nice and level. The only problem I worry about is if that ends up being to high and I wanted to drop it one hole I can't. I guess I am looking for someone to (for lack of a better term) hold my hand and say go ahead and mount it two holes up and it will be ok. That is why I am posing these questions. I agree about the jack plate just wondering if anyone has used one in this application. I just want to get it right the first time.
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| Tom W Clark |
Posted on 09/11/09 - 8:55 AM
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If you want to keep your options open, then drill it for a "one hole up" position. On the smirked hulls, you can drill straight through the transom and hit the splashwell. You will need to modify your bottom washers to fit the shape of the splashwell, but that is easy to do.
You could also cheat the whole layout up a wee bit. There is nothing wrong with the top holes being centered only 1-1/2" down and that would gain you another 1/4" or so.
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| bottomfish |
Posted on 09/11/09 - 1:40 PM
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Tom, I was thinking the same thing about cheating up. But that again flirts with the 2 hole up position. What I will probably do is what I intended to do from the beginning. Which is carefully drill the bottom holes to land at the very bottom of the well, cut the washers and go with it. That will allow me to have the most flexability. It just has such a small margin of error that I was hopeing for an idea that I have not figured out yet. Thanks for the input.
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| number9 |
Posted on 09/11/09 - 2:39 PM
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The Honda BF90s have a "outboard transom height" 1.1" longer than "normal" L & X dimensions, 21.1" & 26.1". If mine, my preference would be to drill transom for two hole up mounting to eliminate having to:
"It will be necessary to angle your drill bit slightly upward to ensure these holes enter the splash well. The lower interior transom washers must have a flat ground on the lower half or be bent to ensure the washer does not compress the fiberglass in the curve of splash well bottom."
You don't have to worry about the Honda being too high and most other motors you may want to mount in the future would probably do just fine there. I'd drill for two up, mount three up.
Bill...On the Ogeechee
1984 Outrage 18...Yamaha T50...that's right, 50hp |
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| bottomfish |
Posted on 09/11/09 - 5:05 PM
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#9, if I drill for the 2 hole up position hitting the slashwell should be no problem even with no angle. I guess I just don't want to end up to high. Looks like I will find out next week as I should be ready to drill by then.
Thanks
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| Tom W Clark |
Posted on 09/11/09 - 7:42 PM
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No, no, no. If you cheat the holes up you can easily drill for "one hole up".
The last Montauk (smirked hull) I had was drilled for only one hole up. Those bolt holes were angled but the lower washers cleared by a mile. I think you could drill for "one hole up" and not angle at all if you modify the washers.
If you cheat the holes up a bit, it should be no problem at all.
I still recommend the Honda be mounted "two holes up" though, even if the holes are drilled to accommodate a "one hole up" position.
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| number9 |
Posted on 09/11/09 - 7:49 PM
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Wayne, also looked at your project album and saw how low the Honda was. Probably close to an inch beloww the bottom and three holes up is only 2.25" difference putting you close to one inch above, very conservative by most current practices. Motor on my Outrage is mounted about 3.5" above bottom because of necessity, it's a 21" L shaft on a 25" transom, only negative is it will blow out unless reducing speed in sharper turns, not an issue in your case. When mounting that motor I really had no clue if it would work well other than reading stuff about performance improvements, mounting height and then making the realization my 20" L was actually 21". After reading about the mounting issues with some of the older Whalers and my own experience really see no negatives to drilling for two up mounting. It'll look better, hole won't be angled and get the bolts our of the bottom of the slash well helping to prevent corrosion. If you were satisfied with the boat/motor before you'll be more than happy and not too high. What ever you decide to do, good luck and enjoy. Bill
Bill...On the Ogeechee
1984 Outrage 18...Yamaha T50...that's right, 50hp |
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| Joe Kriz |
Posted on 09/11/09 - 8:35 PM
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number9,
I have never seen an Outboard manufacturer sell a 21 inch shaft.
Or are these your measurements?
Please post a link.
All manufacturers list their Outboards as either:
15 inch Short Shaft,
20 inch Long Shaft,
25 inch Extra Long Shaft,
30 inch Extra Extra Long Shaft,
You've got some oddball at 21 inch....... Who makes that?????
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| bottomfish |
Posted on 09/11/09 - 8:47 PM
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Tom and bill, I was convinced before to drill at the one hole up position as I wanted my options open. With this discussion and what I have read it seems clear that I will definitely end up in either the 1 or 2 hole up position. As I always do with my projects I will be very carefull. I plan on making a jig and experimenting before final drilling. I should be able to judge the angle if any that is needed. If it looks to be less than 1/4" I will cheat up to achieve the 1 hole up position. That will ultimately leave all options open. She used to run at 35 MPH on the GPS. I am looking forward to the increased performance. The bottom is all new buffed out gelcoat and I plan to reprop when she is back together. I will definitly post the pics on my project page with the outcome. Thanks, Wayne
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| number9 |
Posted on 09/11/09 - 10:01 PM
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Joe,
It's a Yamaha. The marketing information put out always uses the standard S/L/X to not confuse the consumer and you would think boat builders might know but again why put the confusion factor in there The best sources of information are service manuals and rigging guides/manuals. Some owner's manuals also give the actual dimensions. It's common for mid-range (40-90) motors to be about one inch longer and as you you go lower in hp to be as much as 2" longer than standard S/L/X dimensions. Below is a link to my T50.
http://www.yamaha-motor.com/assets/se...26_428.pdf
Would love to have a Whaler 13 with 20" transom to try a Yamaha S length F25 at 16.6" or F15 at 17.3".
Bill...On the Ogeechee
1984 Outrage 18...Yamaha T50...that's right, 50hp |
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| Tom W Clark |
Posted on 09/12/09 - 7:36 AM
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You guys are mixing up two things:
- Nominal shaft length
- The distance between the mounting bracket "hooks" and the cavitation plate (AV plate)
Those two things are NOT the same.
Shaft length essentially designates the height of the transom a given motor is designed to fit on.
The distance to the cavitation plate is usually greater than this and varies slightly from brand to brand and from model to model.
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| number9 |
Posted on 09/12/09 - 11:26 AM
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Nominal shaft length is a very good way to define S, L, X, XL. Advertised shaft length could also be used.
From one of my Outboard Rigging Guides:
"Mercury Marine outboards are advertised as 15 inch (S).....shaft lengths, measured from the cavitation plate to the transom bracket.
NOTE: There are several models that are longer than than the actual advertised dimension."
It then lists a number of 6-125hp motors that range from 1 11/16"(75-125) to 2 3/4"(6-15) longer. The 20-40hp motors fall within the middle of the range.
Whatever we want to call, "The distance between the mounting bracket "hooks" and the cavitation plate (AV plate)" it is important to know information for everyone and especially for those interested in purchasing a motor for re-power. To me "actual shaft length" would be a simple term to use.
I have a "if known then/now know" situation with a F25 tiller L (26.6") shaft and a 16' aluminum v-hull 20" transom boat. In hindsight the S (16.6") would've been a much better choice for my intended purpose and also perform better without having to raise the motor. The tiller has the non-standard mounting bracket with the top clamps so there is no way to get the cavitation plate above or even with the bottom without the use of an additional bracket.
The information is out there but not readily available to the consumer/public and as evidenced by Joe's reply a little known fact that lengths sometimes vary from what's advertised.
Bill...On the Ogeechee
1984 Outrage 18...Yamaha T50...that's right, 50hp |
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| Joe Kriz |
Posted on 09/12/09 - 11:34 AM
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number9,
I was aware that they do vary slightly but not as much as 2 3/4 inches as you mention above.
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| number9 |
Posted on 09/12/09 - 12:10 PM
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Joe,
Only used you as evidence because you suggested 21" was some oddball. Must admit my surprise after looking into the variations over the last couple of years. What I found was even as little as +1" can make a big difference in how one might want to rig their boat or what advertised shaft length might work in a particular situation.
Bill...On the Ogeechee
1984 Outrage 18...Yamaha T50...that's right, 50hp |
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| Binkie |
Posted on 09/12/09 - 9:09 PM
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Whatever the actual length, which varies less than you say, there is a 5 inch difference between S-L-EL midsections. Have you ever measured the distance between the cavitation plate and the center of the prop shaft. In actuality it is the relationship between the prop shaft center and the boat bottom that determines everything. Transom lengths vary also. Most transoms are built at 15 degrees, but the qctual lengh will vary according to the design of the transom, but the vertical distance should be about the same. All this is why testing is important for proper setup.
Rich |
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| number9 |
Posted on 09/14/09 - 7:53 AM
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Yup, there is usually a 5" difference between S/L/X lengths of the same model motor but apparently that is not as many of us think/thought a hard-and-fast rule either. I was able to easily find a only 4" difference between Honda BF40/50A L/X and 2.5" difference on Yamaha T8 L/X. Agree the distance between prop shaft C.L. and the boat bottom in important but most discussions reference cavitation plate distance. Glad that point was brought up because that's another important piece of information that is not readily available and usually left out of the discussions. The Yamaha rigging guide provides the distance from the cavitation plate to prop shaft C.L. Their High Thrust models are sometimes longer than standard versions due to the larger gear housing. That helps to explain why/how my T50TLR advertised as L 20", actual shaft length 21" and additional 0.7" to prop shaft C.L. is able to work on my 25" transom. Without that extra 0.7" the same shaft length F50TRL very well might not work.
All variations from standard shaft lengths were taken directly from Yamaha, Honda and Mercury official publications either available online or from my library of technical publications and are actually sometimes as large as given.
Bill...On the Ogeechee
1984 Outrage 18...Yamaha T50...that's right, 50hp |
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