1998 Glastron

twillyse6

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Aug 28, 2016
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I have a 1998 Glastron 175sx with a Volvo Penta engine. It is rated to go 41 mph @4600 rpm. Best I can get is 34 mph @ 3950 rpm at 4400 ft elevation with a 3 blade 14.5x19 prop. Is there anything I can do to improve speed and power?
 

CV16

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Aug 30, 2007
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You'll want to give better engine and out drive info. There should be a tag on the motor and one on the out drive. You for sure need to get the rpm's up to reach full potential. Is the boat water logged? Did it ever get near 4,600 rpm?
 

twillyse6

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I mixed up my letters in my original post. It is a Glastron 175 SE with a 3.0 135 HP Volvo Penta engine. The outdrive is a Volvo Penta SX Cobra with a 1.97 ratio. When we first bought it from a dealer in Rapid City, it had a 15x17 prop on it and maxed out 33 mph. Over the years it had dropped to 28 mph. We have switched the prop to a 14.5x19 (recommended by in volvo penta's book). Took it out today and it maxed out at 3950 rpm and 34 mph. I raised prop up a little and got 4000 rpm but speed stayed at 34 mph. We have had regular maintenance done on it, run 93 octane fuel with no ethanol in it and add an octane booster to each tank.
 

CV16

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I would have went the other way with the prop and tried a 15.
 

jerryjerry05

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May 7, 2008
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Compression test.
​Load can affect the performance.
How much "stuff" you have on board?
The tests are usually done with the bare minimum and small amount of fuel.
Boat in the water or trailer?
Foam could be waterlogged?
The 41 at 4600 sounds like a prop problem.
Is the prop a Volvo prop or aftermarket?
Sometimes these Volvos need to run their own brand??
 

twillyse6

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Aug 28, 2016
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I bought the new prop (14.5x19) directly from Volvo Penta. The boat is pretty much empty right now as we had planned on selling it before realizing something seemed to be wrong with speed and power. Can you tell me more about the foam being waterlogged? How do I check this? This is my first boat, and although we have used it a lot, all I have done is the routine upkeep, etc. I am learning, but some of this stuff is beyond me right now... Thanks for any and all help!!
 

jkust

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Aug 2, 2008
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So to me you have either lost power or gained weight. There is no reason for octane booster. It literally is like throwing money down the drain. As it is, even the oxygenated free gas which I realize always comes in a high octane variety is overkill for a person who uses their gas and doesn't let it sit.

You will need to test for water intrusion. Surveyors do it with a series of ball peen style hammers and moisture meter along with visual cues.
As for power, the compression test is a good jumping off point. I would also just verify speed with GPS. I will also say that you have some elevation there that you are dealing with that robs power verso the same boat say in my state at 1/4th the elevation. Are you jetted for higher elevation? I get that you are experiencing a downward trend however.
 

twillyse6

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Aug 28, 2016
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Thanks for the information. I will have both the compression test and test for water intrusion done and see where we go from there.
 

jerryjerry05

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The flotation or foam under the floor can suck up water after a while.
​I had a 21 that the transom had gone bad.
I cut it up and the foam was so soaked it weighed about 7-800# more.
The design or engineering wasn't the best on this model.First year and first run.
The inhull drainage was bad and water pooled in some places and held water.

If the boat has set in the water for a prolonged time?? Months and months.
The hull can absorb water and blister.
But I'm thinking this is a trailered boat.
So I wouldn't worry about the blisters and soaked hull.
The altitude might have something to do with it?

Glastron's still in business.
Send them the hull # and the particulars you listed and maybe they can shed some light on the problem???
 

jimmbo

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May 24, 2004
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12,944
Check to make sure the carb is opening fully when the throttle lever is at full. The ignition timing is set correctly, and that the timing is advancing fully as the rpms increase? Has the carb ever been rebuilt? maybe it is due for a thorough cleaning.
 
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