SeaRay 280SS Prop Help

[toger13]

Hi guys

I have just bought a 1998 Sea Ray 280 sunsport with twin 350MAGs in from a place in spain, the boat is spotless inside and out and has had very little use unfortunatly I dont think is has been as well maintained as it looks, this isnt really an issue as I can do this stuff my self

First issue is there is a delay on both engines if the throttle is floored and and is only pulling 4000-4200 rpm WOT it sounds to me like them map sensors are knackerd but I am going to do a comp test and full service first plugs leads cap and arm etc first as I dont know when they were done so I know the engines arnt 100% as they are although they do sound healthy if you know what I mean

Now the main issue its getting huge amount of cavitation/prop slip even if turning pritty steady you have to pull the engines back and turning round quick to get a skiier is a pain, now I have got it out of the water and back to the uk I found it has got the wrong props on

Its got 350 mag mpi with bravo 1 drives 1.5 ratio

When it was new it should have had 3 blade laser II 13-7/8 21 inch pitch
some one has painted the props on it with thick black paint which wont be helping so I have cleaned it off and found it has

A pair of Revolution 4 14-5/8 17 inch pich

I dont know why these have been fitted but there seems a huge difference between a 3 blade 21 pitch and a 4 blace 17 pitch

Laser II`s have been out donkeys should I put a new set of these on as it should or is there something more modern? the forums say this boat should do 60mph on flat water trimmed apropriatly but I do want to pull skiers too

As it is now it easy pulls 2 skiers out but it should with a 17 on it lol

sorry for the babble

Thanks
Si

 

[Tail_Gunner]

Is this a mpi engine or tbi.....First thing's first get the hesitation out..make sure your tach is on all the way thourgh the rpm band there noted to be very inaccurate. I think once that is done you will find your props are dead on a 17 pitch sounds right and a rev 4 is a great prop for heavy loads as to the laser's there not a heavy boat type of prop think bass boat..I cannot fathom why they would be original.

Recently i restored is the word a older 22' offshore style boat every system worked and the engine did sound decent but each of the systems were on the edge of failure and the previous owner just monkeyed it together to keep it running...new carb...new dizzy...the timing had been retarted and the cooling system was barley operating..It took a while but its now in good form.... eye's wide open you never know what you will find.

 

[toger13]

They are MPI so should be 600hp if there both working correctly as I say it should have 21 inch pitch props on from the factory

Cheers
Si

 

[toger13]

Ye you never know when you buy second hand but time will tell

Cheers
Si

 

[Tail_Gunner]

https://drive.google.com/file/d/0B3w...Z2s/edit?pli=1

There's a tutorial for you mag it's probably a mefi 1/2 i would go to the mercrusier forums and get your hesitation out of the picture and again get your tach right and procedd from there. A side note or two twin drive's does not double HP as one might think that but in the end its 300hp.... but twin 300 hp engines can really push it up to the end..here's a example 17p prop...1.5 gearing....4900 rpm yeild's 53mph in theroy and with 10% slip gets 48 mph thats not bad for a 28" boat what about 8000 lbs

Now 21p prop... 1.5 gearing.....4900 rpm yeilds 65 in theroy and 59 with 10% slip.... 60 mph in a 28' boat with 350's is a bit of a reach and only twin drives would get you to 10% slip on a boat that size....I could very well be wrong but probably not...Anyways good luck with the boat it must be a nice ride.

Turn those 17's to 5000 rpm well then add pitch till she drops to 4900

http://www.boattest.com/Partners/Par...oid=161&p=0&s=

http://www.go-fast.com/Prop_Slip_Calculator.htm

 

[toger13]

Ye I won't go splashing out until I have sorted the engines out its the cavitation/prop slip/over reving that I worry about on all the other boats I have had this has only ever happened if I have been trimmed too heigh or have tried to turn sharply on the edge of been on the plane

I have driven a 99 boat in the uk with newer 5.0 260 hp and alpha drives with 19 inch pitch props on and this was fine even on sharp turns ran 48mph untrimed on gps didn't pay attention to rpms though

Thanks for the input by the way

Cheers
Si

 

[toger13]

Boat is quite abit lighter to closer to 6500lbs I tow it on a trailer over here

Thanks
Si