Test on labbed sportmaster!
 

I installed sportmaster lowers on an XZ upper on 36 Skater with stock 500 EFI's. Since the X was already +2 inches, the standard length units were used. We cut 2 inches off the long skegs before we tested. Well, we lost about 3 mph with the same loads, and lost some water pressure.

After some research, we found the stock Bravo lower was much more tapered and flow efficient. So we made the skeg on the sportmaster just like the stock unit and gained 2- 3 mph. The water pickup slots were reshaped so the water could get into the drive and went from 10 psi to 20 plus at high speeds.

Seems as though Mercury has two types of water slots in these sportmasters, long and short. The flush units they sell only work on the short slots. Mine were the long ones which did not work worth a s.....

Has anyone tried this? Does anyone know about why they have these different pickup slots?

After some research, we

John B OK I am heading out to my boat with a saw right now:crazy: :crazy: :crazy: :crazy:




I know you must have some before and after pictures. So let's see them

Wow---that's interesting---nice going on the test! I know this may be a stretch, but would you happen to know what kind of water slots are on the XR drive and/or do they vary with those as well? I take it that you are speaking of the low water pick-up design that is in/at the tip/front of the bullet/casting---right? Thanks.

i think that you would have seen a gain in speed if you had gone with the 2" shorter gearcases.sportmasters were ment to run at the surface,and might slow you down if they are two deep in the water.we are going to do a test on my 37 v-bottom.i will post the results,chris

John,
Any idea how much of the + 2-3 MPH is due to the change to the water pick-up slots vs. the reshaping the skeg? Are you back to the MPH you had with the stock (no nose cone?) Bravo lower case? It would be interesting if you could try the IMCO lower case for a comparison...it's just money. You might jump to 116 MPH!
Sprague

Sterndrive,
The prop shafts were and are now 2 inches above the running bottom surface of the hull. Going up 4 inches ( another 2") is not possible. It's interesting that the hydrodynamics of the sportmaster are not good.
KAAMA and Sprague,
Both the slot and smoothing were done at the same time. I don't think the slot work had much to do with the speed change unless they caused some turbulence. The slip factor on the props was about 1% higher after the changes. We may have too much water pressure now (one leg had 30 psi), some may be overflowing the holes causing turbulence and prop slip. Obviously the original stock units had just the HD type low p/u slots, they were not the XR lowers.

I will attach some pictures later.

I put 2" shorter sportmasters on my 30' Spectre Cat and picked up 10 MPH over the ZX Lowers with nose cones. I liked the idea that I still had the same amount or a little more sked in the water and feel comfortable about the boats control at all speeds and water conditions.

I would be curious to know how much thinning the leading edge of the skeg some would improve top speed. I am getting about 15-18 lbs of water pressure at high speeds. With the stock units I was running 35+ pounds. I also notice a difference in my stock vs lab props in water pressure. My lab props are set up for more stearn lift and result in less water pressure.

More comments on shaping the skeg, please!

Picture side view after reworking

sportmaster Front view reworked

Note leading edge compared to stock. Slots were deepened to increase water pressure from 8-12 lbs, it may to high, max now is near 30 at 110 mph.

Picture of the boat, with cut down cavitation plate. Gives a rooster tail like a 6 drive.

John,
Some have reportedly picked up speed by blocking off the outside water pick up slots. It may also bring your water pressure back down. It seems to me that a little sandpaper and some Bondo would work for a relatively easy low cost test.
Sprague

Thanks, I'll try that next.

why don't you guy's just plug the holes and pick up water elswhere. then you would eleviate all of your issues in one shot. then you won't have any prop disturbance.

Treadwell

Eric, Good idea, however we have lots of long weeds were we keep the boat and I was getting really tired of cleaning sea strainers on my last boat on almost every outing. The Bravo pickups are a great idea if they can be designed properly. This shouldn't have to be a customer fix, in the driveway!

John B.: Send me an e-mail with your phone #. I am very interested in your work on the sportmaster lower.

[email protected]

john,

good point. i would have to agree.

Treadwell

What do you guys feel the speed difference would between transom water pickups and nosecone water pickups?
John B those water slots do look a little strange to me. Are they stock merc?
This is what an outboard sportsmaster looks like

another view

you would probabley gain 5-10mph ( depending on the boat of course)

here's why. if you fill in the holes there will no loger be disturbance to the prop. if you call mercury and get the specs to the lower unit and sand it to spec that alone is three mile an hour.with the longer skeg you can raise the x dimension or go with the shortie. do not shorten the skeg. you will lose handling.
Treadwell

there is one trick if you don't want to go throught all that stuff.

as the slot comes in and stops continue the slot so the water continues throught. this helps lower the water pressure and disturbance to the prop.

Treadewell

Eric, Here is a front view. Should we fill the outer holes or continue the slots ( 2 outer or all four) toward the prop?

Eric are you saying that a GAIN of 5mph is possible by filling in nose pickups and adding transom pickups? I know I would be able to raise my motors. Please explain more about sanding the lower to merc specs.
Thanks Michael

Eric???

How about this? Half as much water going in at speed and relief for excess pressure. Two extra holes if you you get into the weeds!

Boy, it looks ugly......Any thoughts?

Maybe a test after the hurricane goes by.:crazy:

Reduced water pick-up test
 

John,
Have you had a chance to test your modified water pick-ups?
Sprague

Was going today but it's raining! And rain forecast tomorrow, 55 degrees, Geezz.

John,
What is the point of trying to establish top speed based upon changes you have made to your drives when you have 20% leakdown on half of the cylinders in both engines? Have you considered the possibility that your loss in speed has more to do with the fact that your engines are smoked than it does with the drives? Just asking.

Adivanman, It is a good question.

I had a single engine turboed boat that had a leak between two cylinders (head gasket), 30 & 60 psi compression. Top end was still there?? but it idled on 6 cylinders.

Another weird one: 38 Top Gun, ran great top end, also blown (sc), fuel restriction in tank pickup, cooked the piston #7. I had both engines replaced with modified crate 502's. The engine shop got leak down numbers from 30 to 60% on both the old motors. It took me two years to get it to run as fast as the (old leaky) 454's.

:mad:

My conclusion, at 5400 rpm there is not enough time to leak enough compression to loose noticeable power! (within limits of course). What do you think?

I don't run an engine shop, but I wonder about a leak down test numbers for determining when to rebuild. And yes I certainly wish mine were better. I believe any possible loss has been gradual.

John B

John,

I am sorry but I do not follow your analogies and I am really not sure where you are coming from.

In your the other post, you were of the opinion that there was something wrong with the 500's that was out of the ordinary - 20% leakdown past the rings - on the center four cylinders of both motors. You were concerned about your plugs which appeared fouled and, in the cylinders with the leakdown issues, contaminated with oil. At the time, this was quite a major issue for you. Now, the leakdown issue is a non-issue - you've had worse anyway.

Good luck with your testing, hopefully you can find some of the speed you have lost. By the way, did you try a top speed run with the lowers before you modified the skegs?

Adivanman,

In the two examples, the motors were rebuilt. In both cases there was no speed gain.:confused: My question is: how much horsepower may be lost with this much leakdown? My experience has been (minimal).

When I replaced the stock lowers with the same length Sportmasters, we lost 3 mph from the last test. The motors had about 2 more engine hours between the tests. On the first sportmaster test the extra two inches of skeg length had been removed. We put another 10 hours on the boat with varying loads and weather conditions, and the loss was verified.

Then we serviced the motors and found the plug problem and ring seal deal. Black spark plugs are not as expensive a problem as worn out piston rings.

You seem to be knowledgeable on motors, so I'm trying to learn cause and prevention. I didn't expect this type of problem on factory stock packages.

A couple weeks ago we reshaped and sharpened the skegs and modified the water p/u holes. We tested once and gained 2 mph back (apparently).

Sometimes I wonder why I GAF.


Thanks for your interest.

John B. I like that (GAF) I'll use that again. Your testing is what the people ojnthis board benifit from. I can see adivanman's point at times I just think communication is the thing here. We are all tryig to solve problems on this board and its a great resource for answers to our problems that local marinas usually cant handle. All you guys keep it up and have a great time thanks. Greg