hi all... I went to look at a grady today to purchase.. went i took her out for a sea trail it ran great, but with wot i got it up to 5000 RPMS but my speed was only 28 mph... any help would be apprciated
HELP ... high RPM'S low speed
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Need more info. Engine info, boat info? Too small of an engine on too big of a boat and that could be about all you get.
Bottom condition of boat? Acceleration vs RPM's - seat of the pants? Compression?
Bottom condition of boat? Acceleration vs RPM's - seat of the pants? Compression?
Parthery
GreatGrady Captain
How were you measuring speed? If from the speedo its possible / likely that the pitot tube hole on the front of the lower unit needs to be cleaned out.
If you got 28 on the GPS was it knots or mph? At 5000 rpm you should be in the neighborhood of 40 mph. I've owned that same rig and top speed is 43-44. Knots converts out to a lower number.
If you got 28 on the GPS was it knots or mph? At 5000 rpm you should be in the neighborhood of 40 mph. I've owned that same rig and top speed is 43-44. Knots converts out to a lower number.
OK, cool - you've got the proper engine on that boat.
I'm going to ditto what Parthery said about pitot speed vs GPS. If you happened to notice the speedo needle taking longer than it should to come back down, then it's DEFINITELY a clogged hole. A small drill bit, turned by hand into the pitot hole, will fix the problem 99% of the time.
If this was GPS... then we're back to either operator error (not trimming the engine up) or there's another issue... For example, a banged up prop or a problem with the engine like low compression.
If I may make an observation... The reason you're asking these questions may be because you're on the beginner end of the spectrum when it comes to engine maintenance/service? Of course, there's not a thing wrong with that - we were all at that point at some time in our lives. But, the best advice I maybe able to give is to have a marine survey done on at least the engine. The important part here is that YOU pay for this - you want the surveyor working for YOU. The (possible) engine issue may be something simple, or it may not. Either way it gives you piece of mind and a bargaining chip when it comes to the sales price.
Now... because you were able to get 5,000RPM's, I'm leaning towards the pitot issue... but weirder things can happen!
I'm going to ditto what Parthery said about pitot speed vs GPS. If you happened to notice the speedo needle taking longer than it should to come back down, then it's DEFINITELY a clogged hole. A small drill bit, turned by hand into the pitot hole, will fix the problem 99% of the time.
If this was GPS... then we're back to either operator error (not trimming the engine up) or there's another issue... For example, a banged up prop or a problem with the engine like low compression.
If I may make an observation... The reason you're asking these questions may be because you're on the beginner end of the spectrum when it comes to engine maintenance/service? Of course, there's not a thing wrong with that - we were all at that point at some time in our lives. But, the best advice I maybe able to give is to have a marine survey done on at least the engine. The important part here is that YOU pay for this - you want the surveyor working for YOU. The (possible) engine issue may be something simple, or it may not. Either way it gives you piece of mind and a bargaining chip when it comes to the sales price.
Now... because you were able to get 5,000RPM's, I'm leaning towards the pitot issue... but weirder things can happen!
I know alittle about boats ,but u are correct fairly new,and far from a seasoned caption... the RPM and the MPH were measured by the factory yamaha gauges on the dashboard.. the owner said he has the boat for about 8 yrs and it was always like that. the prop was in good shape no nicks or chips
Even if the gauge was showing knots, that only converts to about 32/33 mph. While I've never ran that boat with that engine, I've run enough boats to know that it doesn't sound right. Given the first hand experience by Parthery, something is definitely amiss. Start easy - by verifying with GPS and trimming up properly.
Good luck - I hope it works out for you. But, don't get emotionally attached to the boat and rush your decision. There are more boats in the sea!
Good luck - I hope it works out for you. But, don't get emotionally attached to the boat and rush your decision. There are more boats in the sea!
Parthery
GreatGrady Captain
Do you have an iPhone? If so, download the Navionics app (free). Then run the boat. It will use the phones GPS to tell you how fast you are really going. Or - if the boat has a GPS, pull up the speed display and see what your actual SOG (Speed over Ground) is. If it's in the 40 mph range, then the speedo is off because the pitot hole on the gearcase is clogged. Very front of the gearcase and very small...feel with your finger to find it and then clean it out with either a tiny drill bit, a piece of wire leader, or a small paper clip.
The 5000 RPM is another issue. If the motor is trimmed all the way in, that's about all you will get. Try trimming it out a bit and see if the RPMs increase. My 208 would get to 5500 which is max recommended RPM, but I had to trim it way out. At 2 bars or so I'd turn 5200-5300 which is perfect.
Keep us posted and let us know what you find out.
The 5000 RPM is another issue. If the motor is trimmed all the way in, that's about all you will get. Try trimming it out a bit and see if the RPMs increase. My 208 would get to 5500 which is max recommended RPM, but I had to trim it way out. At 2 bars or so I'd turn 5200-5300 which is perfect.
Keep us posted and let us know what you find out.
thank u guys ... i will check those issues like u said .. what do u guys think, could it be a under size prop. i think it is a 15x17. or to much bottom paint. T he owner said he always power washed and painted the bottom every year , but never scraped or sanded the bottom ...thank u
Parthery
GreatGrady Captain
I think you have the right prop. You need to trim it up a bit which will get you closer to 5500. And I think the pitot tube is clogged. Let us know.
boat will get up to 5000 rpms but speed is only 28 mph... do u think to much bottom paint will cause drag
Clean bottom paint won't be the issue. Most people use ablative, anyways. What type does he have on there?
Parthery
GreatGrady Captain
-you could possibly have a hub going on the prop, although from my experience when you hit it WOT the boat will not plane and the engine RPMs will shoot way up.
-you may be out one cylinder or have low compression in one cylinder.
If you like the boat enough I would have a seasoned tech come check it out. Verify that you have the correct prop.
-you may be out one cylinder or have low compression in one cylinder.
If you like the boat enough I would have a seasoned tech come check it out. Verify that you have the correct prop.
Do you guys think its possible that the transduzer is not level.. the owner said he moves it sometimes when he loses his depth reading
hi parthery... i went to the app store on my iphone to download the navionics , and they give you 5 chioces of different apps. Do you know which one it is to check my speed [mph] thank u
Anything's possible with the ducer. I wouldn't stress over that one - that's a minor issue.
Another option for GPS apps (the boat doesn't have a GPS unit?)... Just search for something like free GPS speed app - or something like that.
Another option for GPS apps (the boat doesn't have a GPS unit?)... Just search for something like free GPS speed app - or something like that.
Parthery
GreatGrady Captain
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FWIW, the pitot tube on my boat always reads 1-2 knots slower than the GPS says when on plane and always reads 1-2 knots faster when at trolling speed. My favorite is when it says we are doing 4 knots when tied to the dock. It's been that way for the 16 years I've had the boat, and I've long given up trying to make it more accurate. Nothing worked. Occasionally it will get clogged, or get an air bubble in it, but in that case, it usually says we are doing 8-10 knots when we are actually doing 24.
For something to compare to... with a 175 HP carb'ed Yamaha, 15x17 prop, and bottom paint, here are my approximate numbers in typical nice sea conditions (i.e. not flat glass, but also not pounding through chop or worried about launching the boat over a swell):
3600 RPM = 17-19 knots (20-22 mph), depending on how much weight we have on board between fuel and a 32 gallon Kodiak bait tank on the deck.
4000 RPM = 20-22 knots (23-25 mph)
4200 RPM = 22-24 knots (25-28 mph)
4400 RPM = 25-28 knots (29-32 mph)
5300 RPM WOT = 30-31 knots (34-36 mph)
For something to compare to... with a 175 HP carb'ed Yamaha, 15x17 prop, and bottom paint, here are my approximate numbers in typical nice sea conditions (i.e. not flat glass, but also not pounding through chop or worried about launching the boat over a swell):
3600 RPM = 17-19 knots (20-22 mph), depending on how much weight we have on board between fuel and a 32 gallon Kodiak bait tank on the deck.
4000 RPM = 20-22 knots (23-25 mph)
4200 RPM = 22-24 knots (25-28 mph)
4400 RPM = 25-28 knots (29-32 mph)
5300 RPM WOT = 30-31 knots (34-36 mph)