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250 Sig Speeds w/300hp 350 Mag MPI


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Another thread about another boat got me back to thinking about the performance of our boat. There is very little information online in regards to the performance of the 250 Sig. What I'd like to know is whether the speeds that I have recorded are appropriate for this boat/engine combo. I'll post the stats below and would be interested in what you all think:

Boat is a 2008 Chap 250 Sig with Mercruiser 350 MAG MPI (300hp)

Boat is exactly 27' LOA and weighs (dry) 6,900lb according to Chap (I know that doesn't include gear, etc.)

I am 6'4" and 250lbs and I typically have about 550lbs of pax on board (including myself)

I do not know the pitch of the prop

All data below is with trim tabs up and outdrive trimmed

Here are my GPS speeds and estimated fuel burn:

RPM GPH MPH MPG

1,000 1.5 2 1.33

1,500 2.5 4.5 1.80

2,000 4.5 7 1.56

2,500 6.0

3,000 7.5

3,500 10.0

4,000 12.5 24 1.92

4,500 16.5 31 1.88

5,000 23.0

What do you all think? I would have thought I'd be a little quicker.

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The MPH looks low and GPH looks high but it is 300hp engine on Sig 250 ... I have no real way to evaluate.

Just to give you some other numbers ...

375 hp, 8.1L engine on 2007 Sig 270 (LOA 29') ...

trimmed (drive and tabs) to the conditions, grubby bottom (end of season) ...

otherwise the MPH would be 2-3 MPH higher on plane at 3000 RPM and above.

Sorry, the table is hard to follow as the samples are organized in columns.

post-11046-0-12351200-1420647096_thumb.p

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Where on the hub? I can't seem to make anything out from these pics, but can you estimate the pitch by looking at it?

IMG_4861.jpg

IMG_4860.jpg

Is that corrosion on the drive or just algae/growth? If corrosion you need to have the drive repainted and anodes replaced.

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Are they the same props that came on the boat? Has the boat always been slow to plane and struggling for WOT? If the answers are yes I would try Four By 4 Merc - Four Blade Set - 18 Pitch. Call a prop shop and talk to them.

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Are they the same props that came on the boat? Has the boat always been slow to plane and struggling for WOT? If the answers are yes I would try Four By 4 Merc - Four Blade Set - 18 Pitch. Call a prop shop and talk to them.

I am the third owner, so I can only assume the prop is original. It's hard to say if it "struggles" to get on plane since I really don't have a baseline to compare to (except for very light and overly powered bass boats). Generally, I don't believe it struggles. There have been a couple instances last summer when it was definitely struggling to get on plane, but I had a good load of people and fuel and the trim tabs solved that. I will get a new bottom job this winter/spring, and I know that will add a couple knots too. But otherwise everything seems to be in good shape in terms of drag and mechanics.

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I owned a Maxum cruiser, a little longer, and the same weight. Exact same engine and drive.

That boat with a 22p 4x4 prop set would do 42 mph with a clean bottom painted hull, and reasonable load. It would roar on to plan like a sport boat. At top speed, rpm was 4800 ish. Cruise was 3600 rpm, 30 mph, and 2.4 mpg.

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The MPH looks low and GPH looks high but it is 300hp engine on Sig 250 ... I have no real way to evaluate.

Just to give you some other numbers ...

375 hp, 8.1L engine on 2007 Sig 270 (LOA 29') ...

trimmed (drive and tabs) to the conditions, grubby bottom (end of season) ...

otherwise the MPH would be 2-3 MPH higher on plane at 3000 RPM and above.

Sorry, the table is hard to follow as the samples are organized in columns.

Looking at your chart and I see very similar numbers to mine, just up to 32mph and the RPM's are very close. Same motor, I believe. Good to see that. Did you compile that information yourself off your boat or is that published stats?

BTW, what's the dry weight of your Sig 270?

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I had an 02 Crownline 242 that weighed 6500 dry with the 350 Mag so the boats are somewhat similar. If I recall correctly it had 24p props on the Bravo III and did 46 MPH GPS at 4900 RPMs on a good day with flat water, 2 people and beer. When your at 5000 RPMS are you at WOT or do you have room to excellerate. Sounds like you need to move up from the 20P prop but you need to know where your at at WOT.

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I owned a Maxum cruiser, a little longer, and the same weight. Exact same engine and drive.

That boat with a 22p 4x4 prop set would do 42 mph with a clean bottom painted hull, and reasonable load. It would roar on to plan like a sport boat. At top speed, rpm was 4800 ish. Cruise was 3600 rpm, 30 mph, and 2.4 mpg.

Good stuff. Thanks, Paul! I noticed your posts in some older threads and was going to reach out to you, so thanks for chiming in. I appreciate that direct-hand information!

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Looking at your chart and I see very similar numbers to mine, just up to 32mph and the RPM's are very close. Same motor, I believe. Good to see that. Did you compile that information yourself off your boat or is that published stats?

BTW, what's the dry weight of your Sig 270?

Hatem, those numbers are all mine. I searched everywhere for some performance stats for this boat. None seem to exist. I took the readings mostly on the same day, but one or two of the data sets may have been on another day when I was experimenting. I've set up a performance spreadsheet so I can run these sort of tests from time to time to see if there has been any noticeable change and also as an initial gauge as to whether everything is set up right or not. I keep hearing about these 40+ mph speeds and I think that will really help when we tube again this summer. Performance seemed a bit lathargic when pulling a tube and additional pax on board, but hey more weight = less performance. I get that.

It's a 250 Sig (really the same boat, I believe), but the dry weight is 6,900 lbs according to Chap. I haven't weighed it, though. Need that dang trailer!!!

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I had an 02 Crownline 242 that weighed 6500 dry with the 350 Mag so the boats are somewhat similar. If I recall correctly it had 24p props on the Bravo III and did 46 MPH GPS at 4900 RPMs on a good day with flat water, 2 people and beer. When your at 5000 RPMS are you at WOT or do you have room to excellerate. Sounds like you need to move up from the 20P prop but you need to know where your at at WOT.

Great info, thanks! WOT, I can get up to about 4700 RPM if memory serves. Takes a while to spool up there, but I think I'm at about 32MPH or so at that RPM. Again, going off memory and I wasn't trying to get a WOT reading.

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Hatem, those numbers are all mine. I searched everywhere for some performance stats for this boat. None seem to exist. I took the readings mostly on the same day, but one or two of the data sets may have been on another day when I was experimenting. I've set up a performance spreadsheet so I can run these sort of tests from time to time to see if there has been any noticeable change and also as an initial gauge as to whether everything is set up right or not. I keep hearing about these 40+ mph speeds and I think that will really help when we tube again this summer. Performance seemed a bit lathargic when pulling a tube and additional pax on board, but hey more weight = less performance. I get that.

It's a 250 Sig (really the same boat, I believe), but the dry weight is 6,900 lbs according to Chap. I haven't weighed it, though. Need that dang trailer!!!

Sorry, TP, I was quoting Richard W.'s chart not yours, big guy. I have the same motor he does (VP 8.1Gi) and his boat is the same LOA as mine also (29'-1") but since his is a cuddy cabin, I'm guessing it's probably a little heavier so it made me think I should really pounce on mine and get some numbers since it's a bowrider and should be lighter than his? Not sure. Waiting for Richard to tell us his dry weight and compare it. Supposedly mine is 6,700 lbs dry and I just round it off to 7,000 lbs with gas and water and maybe 1 person. I was told I should be somewhere around 54-56 top end? Not sure.

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Sorry, TP, I was quoting Richard W.'s chart not yours, big guy. I have the same motor he does (VP 8.1Gi) and his boat is the same LOA as mine also (29'-1") but since his is a cuddy cabin, I'm guessing it's probably a little heavier so it made me think I should really pounce on mine and get some numbers since it's a bowrider and should be lighter than his? Not sure. Waiting for Richard to tell us his dry weight and compare it. Supposedly mine is 6,700 lbs dry and I just round it off to 7,000 lbs with gas and water and maybe 1 person. I was told I should be somewhere around 54-56 top end? Not sure.

Ahhh....sorry about that. Yeah, that's a cool chart he posted.

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So your WOT is only at 4700 RPM. If that's the case your props are too big. So maybe a 19 P 4 blade is what you need.

Problem is not too many places let you try them out before you buy. So being a dual prop, it's a $700 trial and error test drive.

I'm not sure what size my props are. I'll have to check the next time.

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Hmmm....the Mercruiser site gave me the part number (8M8022350) and I find it on ebay, but it's for only one prop? Do I use the back prop and just switch it out with this one? I'm not pulling the trigger yet, but trying to understand if that part number is for one or two propellers or if I retain one of the stock props. Here's the emay link: http://www.ebay.com/itm/NEW-OEM-Mercury-Bravo-III-Propeller-48-8M8022350-14-4-x-19-RH-SS-3-BL-Rear-/330953751548

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Props are replaced as a set. Not sure what's up with your part number search.

I had great success with Ron Hill 4x4 SS props. I sent him my spreed,rpm, boat details, etc. data info, and he made a recommendation. Also agreed that if he was wrong on his selection (which he was not) he would allow me to switch them for a different set, and just pay shipping.

Maybe my experience with him is unique, but I highly recommend emailing / calling him to discuss.

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Props are replaced as a set. Not sure what's up with your part number search.

I had great success with Ron Hill 4x4 SS props. I sent him my spreed,rpm, boat details, etc. data info, and he made a recommendation. Also agreed that if he was wrong on his selection (which he was not) he would allow me to switch them for a different set, and just pay shipping.

Maybe my experience with him is unique, but I highly recommend emailing / calling him to discuss.

Thanks, Paul. Our boat is in the water 99% of its life. Wonder if they make that prop in a non stainless? Seems all the 4x4 props are stainless.

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