Sundowner 205 prop

[chris111179]

Now that I have my trim tab situation under control I would like to tackle my prop situation. Or lack there of….. I have a 1990 Sundowner 205, repowered with a 2011 4.3l TKS + 1.62 ratio Alpha One Gen 2. The current prop that is on the boat is a 15.25 x 15p aluminum 3 blade. It has a few small dings in it. The boat performs great as is on the hole shot and seems to have plenty of torque to get out of the water easily. It does top out at about 37-38 mph which I have seen is a little low. RPMs are on the high side as expected when going wot. My question is if I was to swap to a SS prop, can I use the same size and expect the same performance? I was thinking of going to a 15.25 x 16p to get a little extra top end out of the boat. I do not tow anything and use the boat to fish offshore and to cruise the ocean. I would like to put a fresh new one on and keep the other one + hub as a spare on board.
Thanks everyone.

 

[QBhoy]

Hi. I’d guess that you’re a touch under propped perhaps. Always a difficult one to get right, if you are on the limiter and also given the unusual prop size you have on her now. Large diameter thing, sounds like. Further more, it’s damaged too, making it an unknown quantity as a reference.
Personally I’d see if you can borrow a more generic prop, like a black max 17” 3 blade or similar. I’d hazard a guess that it might be something around that you will be after perhaps. It will at least give you a broad span of reference to go from. Anything less than that in pitch and you are into big diameter things like yours and the 16x16 type. A black max 17”, although being more pitch than you have, will have a smaller diameter, perhaps offsetting any worries or concerns over too much pitch. That’s where I’d be anyway. Then you could go for a stainless prop if you like. But always a guessing game if you are on the limiter and other things mentioned above.

 

[Scott06]

You don’t say if you can get to WOT without the engine hitting rev limiter ? I assume you run out of rpms before getting throttle wide open ?

As outlined above u likely need more pitch either 17” or 19” would definitely recommend roughing things in pitch wise before u spend on stainless

Best bet find a prop shop or dealer who will let u try some props out before buying. Did a dealer do the repower for you ? Was thinking they would be willing to work with u a given the spend on the engine.

 

[chris111179]

You don’t say if you can get to WOT without the engine hitting rev limiter ? I assume you run out of rpms before getting throttle wide open ?

As outlined above u likely need more pitch either 17” or 19” would definitely recommend roughing things in pitch wise before u spend on stainless

Best bet find a prop shop or dealer who will let u try some props out before buying. Did a dealer do the repower for you ? Was thinking they would be willing to work with u a given the spend on the engine.

Not hitting the limiter but darn close. Dealer repowered it back in 2012, with a new 2011 unit. I went ahead and ordered a 15 x 17P by Blackmax as recommended. It was less than $200 out the door. If the 15 x 17P works well, can I do a direct swap to a 15 x 17P Stainless and turn the same RPMS.

 

[Lou C]

I have a similar size boat (1988 F/W H-200), same hull with different top cap (H-200 is the bow rider, Sundowner is the cuddy cabin). Mines got a pre Vortec 4.3 4bbl with a Cobra drive with a 1.68:1 ratio. I’m running a 15x17 alu prop and it performs about the same as yours, perhaps a bit slower due to years of bottom paint build up. I stick with the alu because it’s moored in salt water & less chance of galvanic corrosion without a big hunk of SS for the prop instead of alu.
I tried a 15.5x15 alu and it performed better out of the hole but limited top speed more & I had to watch not to over rev it (I would not take one of these 4.3s over 5,000 rpm due to the split journal crank even WITH the balance shaft). The main limiting factor in 4.3 performance vs the V8s is that. The harmonic vibrations and smaller con rod bearing area due to the split crank journal are the limiting factors.
Interestingly when Mercury designed their “all new” 4.5 V6 they reused all this decades old GM engineering that goes way back to GM having to build a V6 with the same tooling as a V8; that led to the need for the split journal crank to get the vibs mostly under control; and of course they later added the balance shaft to get rid of all of it….

 

[chris111179]

Took me a little longer then expdected but. I installed the 15 X 17P and took it out on a rather choppy day on the lake. Boat didn't seem to loose any holeshot. But picked up 2-3 mph and WOT was right at 4800. I was able to cruise at a lower rpm which was nice for a change. I am running a new set of trim tabs which is probably what allowed me to plane at a lower speed. But between the new prop and trim tabs. It is much more comfortable in the chop.