290 nosecone.....what a drag

[halvecta]

So does anyone have any experience with nosecones on the 290 (or 270,280) drive? It seems I have hit a wall with my drive. It currently has a nosecone that was already on it when I bought the boat. After some major valve, cam and carb work, I seem to have hit a wall. Here are the numbers with different props...

27 3-blade 59 mph 4800 RPM
22 4-blade 58 mph 5000 RPM
23 3-blade 62 mph 5500 RPM

By my calculations and HP, I should be in the upper 60's, touching 70.

The slip is significantly increasing as I gain RPM. My nosecone is worse for wear, and I do not have noticeable hook in the hull. So I am planning on taking the nosecone off and just cleaning up the original lower unit. All I can surmise is that the nosecone shape and lack of smoothness (there is a bit of a cavity on bullet) seems to be working against me at this point.

Any thoughts out there? :confused:

[Pismo]

My old boat had no hook at the dock or on the trailer/blocks but it had a good hook underway because the bottom and transom were so soft. How old is your boat?

[mrfixxall]

Mark, i have told you a thousand times,,,Buy a donzi and give that Halette a rest :)

when i did your motor i recommended changing the exhaust, i would get a set of emi's and let that motor breath a little more.. those volvo manifolds are restricting the power..after you change them then start playing with props :yes:

Sharpen the leading edge of the skeg so it can load the prop with non airated water also i took 1/2'' off the back of the skeg so the prop will load up with water better and lesson the slip..You seen my boat go so now their you have it, all my secrets are out :)

http://cgi.ebay.com/ebaymotors/Volvo-Penta-AQ-22-Pitch-Propeller-853788-872009-_W0QQcmdZViewItemQQhashZitem56277b226fQQitemZ37002 9568623QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear

[mattyboy]

what nosecone?? the solid one that blocks the water intakes on the drive or the one that doesn't cover the water intakes?? is it on straight??? is the nose cone damaged by cavitation burns???

[MOP]

Water flow around the gear case can be disturbed by the damnedest things, years back I did a number on a prop by having and extra gasket on the oil drain screw. I had a burn mark that looked like it was sand blasted, it was fairly deep thank goodness it was a not to expensive prop. It ended up in the trash! I bet you will run better with the cleaned up stock nose.

Phil

[halvecta]

Mark, i have told you a thousand times,,,Buy a donzi and give that Halette a rest :)

when i did your motor i recommended changing the exhaust, i would get a set of emi's and let that motor breath a little more.. those volvo manifolds are restricting the power..after you change them then start playing with props :yes:

Sharpen the leading edge of the skeg so it can load the prop with non airated water also i took 1/2'' off the back of the skeg so the prop will load up with water better and lesson the slip..You seen my boat go so now their you have it, all my secrets are out :)


You rock Mikey! Motor is still strong. Did a valve job, went up to an 850 cfm carb and put a bit taller cam. It is running great, just haven't been able to break her free. Tested a 23 bronson 3-blade today. Really liked the prop, let the heads breath a bit and got RPM up to 5500. It even let me trim it out to 10 and still had a nice set, just not much more on the top end. I am thinking it is definitely something to do with the drive holding me back. The nosecone is real beat up and the bottom of the leading bullett is very flat from rubbing on driveways from before you swapped my leaf springs up.

When you coming out to CA! Get out of that rain and humidity.

Glad to hear you are still well.

[halvecta]

Fixxall, I will keep you posted. I am also waiting to try a few props from Grizz when he is back and able to get some out here. Seems he is on the rebound.

[MOP]

An 850 on a SB is not doing you any favors.

[BigGrizzly]

My nose cone is a hydromotive and has the water intakes in it. I did test before and after.the install, before we had the new props and with the Ron Hill 23 and had no los just a lettle less cavitation and less wandering at idle. Now the exhaust is another story.

[mrfixxall]

An 850 on a SB is not doing you any favors.


mop its a 454 bbc :)

[mrfixxall]

Fixxall, I will keep you posted. I am also waiting to try a few props from Grizz when he is back and able to get some out here. Seems he is on the rebound.


mark, send me a video of your boat running on plane,,i want to see how wet your boat is running..

[BigGrizzly]

Maybe I am doing something wrong my 502 has a 825 CFM, and my origional454 hasa 750 on it.

[halvecta]

An 850 on a SB is not doing you any favors.


It is a BBC. Actually its a 750 with larger bowls.

[halvecta]

My nose cone is a hydromotive and has the water intakes in it. I did test before and after.the install, before we had the new props and with the Ron Hill 23 and had no los just a lettle less cavitation and less wandering at idle. Now the exhaust is another story.


Grizz, my nosecone is very beat up. When I bought the boat, the drive sat very low on the trailer and previous owner had scraped the drive bullett often. In fact, fixxall did a leaf swap on the trailer for me to alleviate that problem. Their is a big flat spot on the bullett bottom and the finish job on the cone is not smooth all the way to the back. There are a number of spots where air pockets could be forming on each side. Once we have it off, we will run again and then consider the Hydromotive if their is any loss.

Maybe when I get a few of your props to test, I will find the magical combo.>:wink:

[halvecta]

mark, send me a video of your boat running on plane,,i want to see how wet your boat is running..


I just tested a Bronson 23 and trimmed out to 10 (had to override the limiter) on my last test. Finally got the boat to break water at the very back. It really liked the rpm, just need to work on dialing in. I think my trim indicator is too conservative, it was keeping the drive tucked in too far even at 4.

Mike, I will make a plan to do this and send it over to you. Or, you could just come on out for a race weekend and see it live.:shades:

[CAPTBEACH]

Lowers are Aluminum I am presuming, at least my Suzuki OB's have Alum Lower Units...

Would removing one and polishing the hell out of it...literally to a mirror finish help? After polishing one would presumably apply about a dozen coats of wax to protect it against corrosion... just wondering...

[MOP]

A matte/sanded finished lower is more efficient then a polished one, the matte helps to break the stiction layer. Some of you remember the cup race off Australia, part way through the race conners had Boeing rivlets flown in. the rivlets Boeing applied to commercial jet liners to reduce fuel usage, they were a clear self stick film with micro Sargent stripes. They applied the rivlets to the bottom and gained 2/10 of a knot, sounds like nothing to a power boater but it makes a tremendous difference when racing sail boats. I raced sail boats for many years, back in 88 I won my division boat overall in a field of over thirty boats off Block Island. I went from a wet sanded baby azz smooth bottom to a stippled finish following Conners move. I was accused of running my engine during a race off Long Island, when the protest committee inspected my "engine less" boat they had quite a giggle! My 22 has the last 1/3rd sanded with 220 to increase efficiency! IE: Smooth is not fast contrary to what most believe!

[halvecta]

Smooth is not fast contrary to what most believe!

I agree. If you look at any of the Merc XR or #6 drives, they are matte unfinished metal.

What I am referring to with the term "not smooth" is dips and cavities that create air pockets. If I run my hand down the side of the unit, you can noticeably feel "dents" that are 2-3 inches long. I get what you are saying, but do you think the having that slightly rough surface as perfectly flat as possible is key? Also, I heard that any nose entry angle that is not straight will be exaggerated an MPH increases.

[halvecta]

My nose cone is a hydromotive and has the water intakes in it. I did test before and after.the install, before we had the new props and with the Ron Hill 23 and had no los just a lettle less cavitation and less wandering at idle. Now the exhaust is another story.

So Grizz, no significant MPH increase with the Hydromotive? I was just looking at their website. How did you integrate the water pickups on the VP? What top speeds are you seeing currently?

[CAPTBEACH]

OK...that makes sense...breaks up the boundary layer...I did the same thing to my sailplanes wings...when I painted it I strove to get the absolute best finish possible on the wings and fuselage...mirror finish...then I wet sanded the wings with 400 to take the shine off of them...to an almost matte finish...I got a significant jump in performance from 37/38:1 to almost 40:1 measured in still air several times...

http://groups.yahoo.com/group/hp-gliders/photos/album/1897779610/pic/1096234737/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc

Lots of similarities at least in flow...so this might be better...

http://cobrapower.com/store/images/DSC02525.jpg

http://groups.yahoo.com/group/hp-gliders/photos/album/1897779610/pic/1096234737/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc

[halvecta]

http://cobrapower.com/store/images/DSC02525.jpg

http://groups.yahoo.com/group/hp-gliders/photos/album/1897779610/pic/1096234737/view?picmode=&mode=tn&order=ordinal&start=1&count=20&dir=asc


Ding, ding, ding! That's the dealio. I am sure Merc has tested and re-tested these various finishes.

[Ralph Savarese]

This week end was unbelevable for donzi testing for me added a new i beleve to be hydromotive nose cone to a 280 drive the boat developed an un beleveable chine walk so bad i could not control the boat removed it and back to normal also dicovered using different bprops found my torque steer to the left rather than right that it has always been

[CAPTBEACH]

Has anyone tried placing turbulator dots around the circumference of their nose cone? I'm reasonably sure they would be helpful to expel the boundary layer after it broke the laminar flow, and also keep the flow more constant around the cone, lower unit and rudder/skeg. Its all about the flow...

[Ghost]

http://www.diyefi.org/forum/viewtopic.php?f=15&t=203

[BigGrizzly]

I have installed several and never found this on a 270 or 280/290.

[halvecta]

I have installed several and never found this on a 270 or 280/290.

Randy, what is 'this' referring to?

[BigGrizzly]

ref.chine walking and pulling isue