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Prop advice for a 90 yamaha two stroke on an 1988 montauk
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| mtown |
Posted on 07/22/15 - 3:29 PM
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Bob,
Sorry I just saw you are in MD also. Let me know if you want me to come by to help. I am northwest of Balt. but also go to Annapolis/beach on some regularity.
Scot
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| Whalerbob |
Posted on 07/29/15 - 6:02 AM
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Mtown, that's a generous offer but I'm probably not going to tackle this until after the season is over. I'm in MoCo about 30 miles west of Baltimore so probably too far to be feasible anyway. Even though it's only an hour or two of labor it's really a 2 day job considering the cure time for the epoxy and gel coat.
My biggest concern is getting those holes right. Do you think the method I describe will work?
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| mtown |
Posted on 07/30/15 - 5:49 AM
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Taking the motor off completely is not necessary. I already had it off the second time and it is easier to drill and patch that way.
The first time, on the 1964 I ran a 2x12 from a beam in my carport to the top of a 6' stepladder in line with the top of the motor. Then used a cable puller to secure the motor. When it was tight I removed the bottom lag bolts.
Then I removed one top bolt and loosened the other so the motor could pivot on the one remaining bolt. I was able to re-insert the other top bolt one hole up at that point. Then I pulled the other top bolt and pivoted the motor to raise the second top bolt one hole. Repeated this process to raise the motor to the third hole up.
Then with the top bolts re-inserted I was able to drill the green holes with the motor in place. Slight upward angle was necessary to get holes into the splash well. It was a while ago, but as I recall the lag holes were below the motor bracket after the motor was raised.
Epoxy thickened with fine chopped glass, or a dowel and epoxy will fill the holes. I used "wet /dry 700" a fairing epoxy compound from Progressive Epoxy the second time. It is super easy to work with and doesn't run at all.
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| jaxmyth |
Posted on 07/31/15 - 3:05 AM
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ok, so I remounted the engine 3 holes up, and i'm still getting around the same performance. i'm only seeing a top speed of 36 mph on the gps. my tach isn't currently working so I cant tell what rpms it's spinning. I do have a new tach on the way. I pretty sure the prop I have is wrong. I currently have a 13 1/4x17 solas new Saturn prop. the hole shot is good and the midrange is good, but top end isn't what it should be. the motor is healthy. i'm willing to sacrifice some hole shot and midrange for top end speed. the stiletto advantage is no longer available. which prop should I get?
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| Phil T |
Posted on 07/31/15 - 3:39 PM
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Don't do anything till you get a tach. You are blind without it.
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| jaxmyth |
Posted on 08/02/15 - 11:08 AM
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Ok, so I got the tach working and I'm hitting 36 mph at wot at 45-4600 Rpms. If I trim up high it revs a little more and begins to porpoise.
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| wlagarde |
Posted on 08/02/15 - 1:20 PM
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Your rpm's sound low. Can you tell us what your engine operators manual indicates the acceptable operating rpm range is?
1976 Sport 15 w/ 2005 50hp Nissan 2 stroke |
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| jaxmyth |
Posted on 08/03/15 - 5:22 AM
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It should be close to 5500 rpms at wot according to everything I've been reading. I'm pretty sure I need to go down in propeller pitch.
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| Whalerbob |
Posted on 08/06/15 - 5:40 AM
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Thank you mtown for the detailed explanation but with my current install I'm pretty sure I will need to remove my engine to fill the bottom holes (1989 Montauk with 1998, 90 hp Yamaha 2 stroke). I have some time this weekend and I'm pretty sure I can do it in my garage with a little engineering.
I'll post a picture later but the bottom mounting on my current engine is a slot as opposed to the top mounting which is 4 holes. Can anyone tell me if the new engines have the same configuration?
If the bottom mounting on new engines is now a 4 hole configuration instead of the slot it adds another level of complexity to make sure I get the bottom holes at the perfect height.
My second minor concern is I estimate the current blind hole is very close to where I will need to drill the new hole. I realize if the hole is filled properly it shouldn't matter but it makes me nervous that the drill bit could drift if they do overlap and I'm boring through two different materials.
Edited by Whalerbob on 08/06/15 - 7:19 AM |
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| mtown |
Posted on 08/07/15 - 5:39 AM
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The bottom is still a slot. My 2007 Yamaha 2-stroke is mounted 3 holes up and the bottom bolt is near the top of the slot. It was mentioned on this thread or another that you can drill the bottom holes after raising the motor and attaching with the top bolts. I did that on this boat and it works. With the motor completely off, I would use the measurements given by Joe and drill the green holes. That is what I did on my other 16' and it worked fine also.
Your splash well is probably deeper than mine but you may have to angle the drill bit slightly upward when you drill. Others with a Montauk of similar age could tell you for sure, or just measure down from the transom notch.
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| Whalerbob |
Posted on 08/07/15 - 5:56 AM
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Thanks again mtown. I started getting it prepped last night and should be done soon. My splash well is deeper then the older Montauks so no issues there.
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| Whalerbob |
Posted on 08/07/15 - 9:56 AM
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Aside from being nominated for the next Darwin award for the way I jacked up my engine... the other concern I had was what I'd find inside the transom. Turns out the top holes were solid and dry but the blind holes were moist inside but the wood is very solid. Not great but sort of to be expected after 17 years since it was installed and if left unchecked it could have lead to more serious issues down the road.
I put a 100w lightbulb outside each blind hole and aimed a small blower / heater in the splash well for now. Hopefully it'll be dry enough by later today so I can get back to it but I'll wait add long as needed.
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| mtown |
Posted on 08/08/15 - 5:46 AM
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Many epoxies will set up in moist or even wet conditions. Progressive epoxy sells a lo-vis epoxy that will set up on a glass of water. Probably West has a similar product. Progressive's wet/dry 700 epoxy putty can also be installed underwater and is much easier to work with. About half way between mayonnaise and peanut butter.
You will only need a small amount. I have half of my gallon kit in my basement. I would be happy to donate some to your repair. e-mail me if interested.
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| Phil T |
Posted on 08/08/15 - 12:14 PM
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Jax -
Before messing with the prop, ensure the throttle linkage is properly set so that with the binnacle throttle all the way forward, the link in the engine is at the stop.
If you are 3 holes up, light load and only hitting 4600, you have the wrong prop.
Having had the exact setup myself, I say go with the Yamaha painted stainless steel or Stiletto. Not a fan of Solas. Remember blade design is different across brands, so an X by Y from Yamaha is not the same as an X by Y from Stiletto.
Yamaha and Stiletto Advantage props work well with Yamaha motors on classic 16 an and Montauk hulls.
With the engine 3 holes up, motor in tune and a good prop, you should see 42-43 mph @5500 rpm with full load of fuel, no gear and just you.
Edited by Phil T on 08/08/15 - 12:18 PM |
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| jaxmyth |
Posted on 08/08/15 - 3:14 PM
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Thanks Phil. That's what I was expecting. The prop that I had on my old 70 Yamaha 2 stroke was the Yamaha 13x17k prop. Is this the same as the Yamaha painted prop? I'm going to try this prop and see if I get anything different. I know this motor has more. It's just not revving like my 70 was. And I actually saw 35-36 top speed with my old 70. I know this 90 should be at minimum above that. Not maxing out at that.
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| Joe Kriz |
Posted on 08/08/15 - 3:36 PM
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jaxmyth wrote:
ok, so I remounted the engine 3 holes up
Jax,
Which holes did you drill in this drawing below?
http://www.whalercentral.com/articles...icle_id=82
For the Montauk 17' hulls (and other 17' models) about 1986 a later, you should be able to drill the "Red" holes as Boston Whaler changed the depth of the splashwell for this reason.
As Always, layout the holes first on both the inside and outside of the transom to make sure the washers do not interfere with the radius at the bottom of the splashwell.
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| Whalerbob |
Posted on 08/08/15 - 5:43 PM
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Mtown, thankfully the holes were dry today so I'll glass them tomorrow with west systems epoxy and chopped glass so I'm good to go.
I had my drain tubes replaced about 10 years ago and they're still in good shape but the guy that did the job said the bottom one was wet. After this adventure I think I'll pull them at the end of the season and let it dry in the garage over the winter.
I'm not expecting much in terms of performance improvement but I'll post my results as soon as possible.
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| tedious |
Posted on 08/09/15 - 7:03 PM
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jaxmyth wrote:. the stiletto advantage is no longer available. which prop should I get?
Jax. I have a 13.25 x 15 Stiletto Advantage 1 for sale. I used it for about 40 hours on my F70 before moving to a different prop; the Advantage is in absolutely perfect condition - not a single scratch or ding or nick on it. It also has the correct Yamaha hubkit for your application.
If you are interested, please PM or email me.
Tim
Edited by tedious on 08/09/15 - 7:05 PM |
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| jaxmyth |
Posted on 08/11/15 - 10:42 AM
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well, I decided to try the old prop from my 70hp on the 90hp motor and there was a noticeable difference in rpms. the prop that was on my 70hp is a 13x17 prop also. I believe it was a Yamaha prop because it has 13X17K stamped on it. is this indicative of a Yamaha prop? with the old prop my rpms went up to 5k and the top speed was 38 mph at wot. I had a decent load in the boat and 20 gallons of fuel.
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| Finnegan |
Posted on 08/11/15 - 12:09 PM
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The Yamaha 2-stroke 90 and the Evinrude E-tec 90 are very similar in actual HP at the prop, and should run neck and neck. They do not use the same prop, however, since they have different gear ratios. Both usually give 40 MPH, maybe a little better, on a classic Montauk. It should also be noted that the prior 16' hulls are lighter and run faster with the same HP, so they are not a good comparison.
Both the Yamaha 90 and Mercury 90 2-strokes use a 2.33 gear ratio. When Whaler was selling these boats factory rigged with Mercury 90 2-strokes, the furnished prop was either a Mercury Black Max aluminum 21" pitch, or a Laser II 20" pitch. So the Yamaha maybe should be able to turn a 19" pitch prop at least, since I do believe the Merc puts out more power than the Yamaha. I don't think the Yamaha 90 can turn a 21" pitch prop like the Merc does.
With the engine raised up, and putting out the rated HP, the fastest prop you can buy for that rig would be a Mercury Laser II in 19" pitch. They give tremendous hull lift and top speed on a Montauk, and are faster than a Stiletto on an actual pitch for pitch basis. If your engine can't turn anybody's 19" prop raised up (or a 17" Stiletto), the engine should be looked at. Sometimes used engines can look nice cosmetically, but are worn out internally.
You appear to be only getting 70 HP out of it.
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