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View Full Version : Nosecone on a TRS, ye or ne and if YE...



pipnit
05-05-2016, 01:54 PM
Hey Guys,

I destroyed my TRS on my '76 2+3. The autopsy shows that there was water in the drive at some point, evident from the pitting on all the gears, etc. This didn't happen on my watch!
Anyhew, I had a nose cone on my old drive and the boat would do 75mph at 5,500 RPM (what the tach read anyhow). I found and purchased a NOS TRS and just called Hydromotive to purchase a nose cone. None available for a month or so. SO then I started to think, is a nose cone even really helping me. Instead of sitting here, scratching my heads, I've decided to reach out to the good people of the Donzi registry. So, what do you guys think? I'm running a hydromotive quad that I believe is 25" pitch. Do you think the nose cone helps or just looks cool? Also, does anyone know who still makes them for TRS drives aside from Hydromotive?

Thanks,

Geoff

gcarter
05-05-2016, 02:57 PM
It's been stated by folks who have a lot more experience than I do, that they start to become effective above 70 MPH.
But even so, you may run a lot faster some day, and screw it! They do look better!

olredalert
05-06-2016, 10:00 AM
----Agree with Georges assessment. Both my TRS's for the Spitfire have nosecones as I expect the speed to be above 70...LOL! Just make sure the nosecone is on straight.......Bill S

woobs
05-06-2016, 02:31 PM
Here's the way I look at it...

1) it does look cool!
2) boats that do 70+mph have to go 1 - 69 first... and they still work through those speeds.
3) If you're not going 70+, what does it matter now? it still looks cool.
4) Your not dead so, someday your boat might just go 70+... be ahead of the curve.
5) did I say it looks cool!
6) if you have the resources... why would you NOT add a nosecone?

... and that's a balanced and objective synopsis. :)

Ghost
05-06-2016, 03:09 PM
Lol, Sean. :)

Just curious, what sort of ingenuity have people come up with to mount the things straight? Seems like it'd be REALLY hard to get right, and that any error would be hydrodynamically disastrous, no?

woobs
05-06-2016, 05:21 PM
In Peterborough, Ontario there's actually a company that does all kinds of marine work from V driveshaft straightening, to sterndrive repair/welding, modifications and prop repair. They will install one (welded) and guarantee it is perfectly aligned. I have seen several of these after installation and you'd swear it came from the factory that way. Although, I'd have to admit... I'm not sure they do Volvos (but, they might).

That's where I will go when the time comes !

gcarter
05-06-2016, 07:22 PM
The TR came w/a nosecone.
The reason is, in 1987, the first Bravo came out and they were about as hydrodynamic as a TRS.
I don't know when Merc improved the shape of that drive, but mine is from that first year.
The nose cone appears to be straight. I have external hydraulic steering, so I probably wouldn't
feel anything anyway. It was applied w/epoxy and seems to be well done.
I haven't any real full throttle runs yet so I can't really comment on high speed improvement.

pipnit
05-07-2016, 08:22 AM
Here's the way I look at it...

1) it does look cool!
2) boats that do 70+mph have to go 1 - 69 first... and they still work through those speeds.
3) If you're not going 70+, what does it matter now? it still looks cool.
4) Your not dead so, someday your boat might just go 70+... be ahead of the curve.
5) did I say it looks cool!
6) if you have the resources... why would you NOT add a nosecone?

... and that's a balanced and objective synopsis. :)


The boat goes 75mph or it did with the last drive (had a nose cone).

Right now, I'm just having a hard time finding one. Hydromotive won't have one in stock for another month.

If you glueing it in place, you can make sure it's centered by using a string.

OFFSHORE GINGER
05-07-2016, 08:59 AM
I have two TRS nose cones that i have never used for sale .

pipnit
05-07-2016, 09:15 AM
I have two TRS nose cones that i have never used for sale .


great, are they both the same? WHo makes them? Are they complete "kits" with epoxy, etc. Asking price? I'll likely buy one if I can. If you want to take it offlist, ringguy at gmail dot com.

Thanks!

OFFSHORE GINGER
05-07-2016, 09:34 AM
I got them when i worked at Skater and if memory serves me right they are Hydro Motive , and not a complete Kit ( Epoxy ) although you can apply them to the Drive using West System which i have done in the past just curious before i look at pricing just how much was H M going to charge you because i will and can beat there price all to hell ? Artie

pipnit
05-07-2016, 03:30 PM
Artie, honestly after he said that they weren't going to have any after a month, I didn't even get a price.

MDonziM
05-07-2016, 05:05 PM
I have nose cones on my bravo drives and the main issue I have had is with water somehow getting in /under the cone and blistering the paint and faring. Having re-installed them the only way I would consider it is having them welded. I have heard that on a bravo the speed benefit starts at 80mph+. Not sure what the number is on a trs. Another thing to consider as to possible performance gain is the expanded running surface can actually cause more drag and possibly cause some lift as well. My bravos are mounted several inches higher than the TRS's which also affects the hydrodynamics of the cones. Bottom line, if you like the look, go ahead and weld them on, but I wouldn't bet on much gain in speed. Years ago I put one on my 16' when I repowered with a 350/280volvo from a 289/250 but that was pre gps and not apples to apples power etc.

Ghost
05-07-2016, 07:06 PM
The biggest hydrodynamic question I have about nose cones is not about side to side angle (which presumably should be dead ahead, and is a mounting challenge, but not a design question).

Rather, my question is about the angle of attack in the vertical plane. It seems like the cone centerline has to be the same line as the prop shaft centerline, such that the cylindrical bulge in the drive is uniformly capped by the cone. Lots of clumsy words there, but I think it's actually simple.

What's not simple is the angle of that drive shaft centerline, relative to the surface, when any given hull is optimally trimmed out for speed. Seems like ideally for minimizing drag from the drive, that angle of the driveshaft centerline would be parallel to the surface of the water. But it almost certainly won't be. It will probably be angled slightly downward, or slightly upward. I'd expect slightly downward, as I'd think that would be generating bow lift and increasing speed with most of our hulls.

If so, a protruding nose cone, running pointed slightly downward, feels like it might create a ton of drag, compared to the "flat front" of a Bravo drive. It also feels like there might be a case for a prop shaft bulge that's was not a pure cylinder around the prop shaft centerline. Or an argument for an adjustable cavitation plate angle, or other fin to pull the drive down slightly, while keeping the prop shaft parallel to the surface.

I always assumed cav plates were parallel to the prop shaft, but maybe not? Feels like the math to actually optimize this stuff might be insanely complicated. The sort of thing that would require s###loads of testing, as with airplane designs in wind tunnels. Anyone know anything about this?

gcarter
05-07-2016, 09:12 PM
Mike, if nose cones were like a point on a missile, I think you'd be correct,
but instead of a "bullet" shape, the whole thing develops into a fairly
broad chisel point as the shape develops moving forward.
So the imagined mis-alignment doesn't really happen.

Ghost
05-07-2016, 09:35 PM
I think I get what you mean, but when I look at the pics, it still seems like there could be a lot of vacuum behind the nose cone if they trimmed out with any real downward angle, no?

84528

Either way, do we know how it is with drives like these speedmasters?

84529

And in general, do we know how much down-angle props shafts usually end up trimmed to? And do we know if cav plates are parallel to the prop shaft?

gcarter
05-07-2016, 10:03 PM
Mike, the only drive I know of w/that problem is Carl's shorty.
But the erosion he's experienced is located further back, and
not under the nose.

OFFSHORE GINGER
05-08-2016, 06:42 PM
Artie, honestly after he said that they weren't going to have any after a month, I didn't even get a price. Well................how about sixty five dollars a piece and you pay for the shipping , and might i mention that these nose cones have a speedo tube built in if you want to use it or just cut it off .

Carl C
05-08-2016, 07:00 PM
Mike, the only drive I know of w/that problem is Carl's shorty.
But the erosion he's experienced is located further back, and
not under the nose.

George, every shorty I looked at at Brian Orlandi's shop had cav burn behind the water inlet. Including one on another 22 Classic. My problem has been fixed after welding up and relocating the water inlet further forward. Also the weld fill is much harder than the original cast aluminum. This is the latest photo I have handy but we have since welded up the rear of the inlet and filled in the cav burn with harder welding rod.
http://i763.photobucket.com/albums/xx275/CARLC222/DSCN4539_zps3d5pqhet.jpg (http://s763.photobucket.com/user/CARLC222/media/DSCN4539_zps3d5pqhet.jpg.html)

gcarter
05-08-2016, 08:09 PM
Well done Carl! That looks a lot better.

pipnit
05-09-2016, 09:20 AM
Well................how about sixty five dollars a piece and you pay for the shipping , and might i mention that these nose cones have a speedo tube built in if you want to use it or just cut it off .

Great, thanks. I only need one, is that cool? Can the speedo tube hole be filled?

Thanks,

Geoff