Formula 206 LS - New to us - Appalling to-speed - need help with prop ??
 

Hello Guys - Greetings from the UK.

Together with a mate - I have finally taken the long-awaiting plunge into Formula ownership with a 1990 206LS.


The boat has a 5.7-litre 350 Magnum, 450 hours, which seems to be in rude health and sounds amazing with the straight-through exhausts.
She has an Alpha 1 Drive, which I gather is stock for these boats.

Over here in the UK we tend to keep the boat in the water, though this one has never been anti-fouled and consequently the bottom was bad. REALLY bad....

I drove it back from where I bought it Saturday just gone, and with the owner telling me she did 45 mph with a clean bottom, I was horrified to see her capable of only 28 mph on GPS
Yes, 28....!!!

We knew the bottom was bad, but seriously, this is not acceptable given the sort of speeds other 206 owners seem to achieve.

We had the boat craned-out to clean the bottom, at which point one of the strops slipped and she came crashing down on the drive. Obviously we were gutted but, it could've been so much worse, however that's another story....

Basically we need some pointers from you guys the other side of the pond about how to fix her up!!


So, some figures as I know this sort of request is meaningless without these...

She was topping out at only 4,100 rpm and 28 mph.
She has a High-Five Prop 21P (I just went and checked) in perfect condition - I know this is not top-speed optimised but again, 28mph....
I am not 100% certain of the ratio, but have no reason to believe it's not 1.5 as stock ?

I was thinking about trying a 21P Mirage or Mirage Plus, as I gather these are "go-to" for this sort of motor and drive?
Unfortunately this sort of boat is fairly rare around here, and so we dont have the luxury of being able to test all sorts of different props, so kind of need some clear focus right away.

I am not hell-bent on all out top speed, but 50 would be nice.
Equally important is cruising speed ecomony, given the cost of motion lotion over here - ~$2.60/litre at the docks (yes, really)

Obviously the state of the bottom is/was a huge factor, but I doubt it would make more than 10 or 12 MPH difference on its own, which is still a long way from where we want to be...
I appreciate you guys in the States don't often have this problem of hull-fouling...

What could've stopped the revs getting higher than 4,100? I would expect minimum 4,500? Could it be a combination of hull-fouling and the High-Five?

We are waiting with baited breath for your wisdom...

Best wishes for now - Nick and Tim

In stock trim the 206 should run 55 with a 350 mag. You may hear 58, but that is maybe with the wind and tide etc. etc. Should be 55 gps. That is with either a 21 laser 2 or mirage non plus. Should turn 4600-4800 ish with those props. The mirage has more diameter so may turn slightly less but speed should be the same. I think that boat came with a mirage stock. Trim her up good, they like bow lift for speed.

A dirty barnacled up bottom will rob 10mph+ easy.

Any other questions just ask, I have owned mine for a while now and know them very well.

Thanks Mr Maine - glad to hear that if anything I have underestimated the effect of her dirty bum.

What about the revs though? Why is she doing only 4,100 rpm WOT ? - Is that the prop and/or dirty bum?
If so great, but if not it's a bit worrying...

If she won't rev beyond that then I'm a bit screwed!
Nick

4100rpms at 28mph with a 21 is over 50 percent prop slip, thats huge. I wouldn't even look at those numbers until the bottom is squeaky clean, you GPS a new speed with a 21 mirage. Trim it up good without a lot of "luggage" on board and see what you get. We'll go from there. If you do some water sports, keep the high 5, otherwise its not the prop you want.

You most definitely need to get the Mirage Prop... but something tells me there is still an underlying issue here.... your RPM's should be closer to 4800 for starters (which could be a prop issue), it is terrible to run a motor out of the recommended RPM range which for you is 4400-4800. After you take Mr. Marines advice, I would start with the timing, the fact that the motor sounds good and you didn't describe any real running issues (carb popping, stalling, strange noises, poor planing, etc.) you may just need to advance your timing which would increase RPM and consequently speed. Your timing should be 10 degree BTDC. The next step would be to check your points (a cheap and recommended replacement) There is a laundry list of things to check here.... but timing is a quick and easy check before you start dumping money into it.

I had an 89' 206LS, its a great starter boat into the Formula family and you will certainly enjoy it...

You should clean bottom, and retry your current prop. without extra weight in the boat, as well as the tabs up (assuming it has tabs) also remember to trim up on plan. I would definitely get a 21p mirage. But in the mean time I would retry what you have to verify the numbers

I have a 1986 206LS with 260hp (owned for 18 years) with a 21p Mirage it goes 58 mph and a little slower with a High 5. Now years back I had a problem with the boat going slower and slower, went on for a couple of years, but the boat engine ran nice and smooth. Turned out to be the carburetor. Had the carb rebuilt, still no go. Bought new one. Problem solved. I would also check simple things like cap and rotor, plugs, timing, Fuel filter and fuel filter screen at carb. That boat should turn more rpms with those props as mine does. Hope this helps.

Hello Chaps.

Just to update you all 8 weeks on......

Boat is being craned back in on Friday morning with a very clean bottom.
Plan is to re-fit the High-Five and go for a run to quantify the negative effect of the fouling / dirty bottom, and I have finally managed to track-down the correct Mirage 21P which is due to be delivered tomorrow.

We would then swap to the Mirage and test top speed again. That way we are able to test both variables independently and see what's what.

Will report back then.

Cheers - Nick.

Nick- I would also hook another tach (like from a tune up kit) and verify that you are getting a correct reading on the boats tach.

Yes let us know the results. My 86 has medallion gauges and when I bought the boat it was a few hundred rpm off, used 2 other tach for comparison and they read the same. Checked to make sure setting was on 8 cyl. It was.
The adjustment screw on the back was super sensitive which is stupid but I got it. 5 years later it is 200 rpm off again.