Whaler Central - Boston Whaler Boat Information and Photos

Posted by wbswhaler on 09/12/23 - 5:16 PM

Engine has 500 hours.
Boat has minimal bottom paint.
30 Gal of gas 2 persons onboard no other gear.
Flat calm lake.
I was expecting to see upper 30 mph
RPMS are good but boat only making 26 miles per hour GPS at WOT and planed/trimmed out (not Knots)

What should the prop pitch be for this boat? and on a boat of that year/hours shouldn't I still be close to the upper 30s in speed?
Thanks in advance.

Posted by Phil T on 09/13/23 - 5:26 PM

Here is the factory performance report.

Note the boat is very light, no load, wind, current etc.

Pull your prop and verify it is a Vengence 13-1/4 by 15.

If this prop is installed and the rpm's are 5800-6,000, I think you may have a spun hub.

Edited by Phil T on 09/13/23 - 5:30 PM

Posted by wbswhaler on 09/14/23 - 5:38 AM

Phil T. Thanks so much.
Can you divulge your source location for this older year spec sheet so I may find others on my own in the future? Oldest i could find was 2015.

Note the boat is very light, no load, wind, current etc.
---If the boat I tested was 400 lbs more because of gear and a single coat of bottom paint, am I right that it is still odd it would loose 15 mph?

Pull your prop and verify it is a Vengence 13-1/4 by 15.
---- It was ,but in rough shape for sure.

If this prop is installed and the rpm's are 5800-6,000, I think you may have a spun hub.
-------I see that the test data shows 2.07 ( 2006) 15p prop vs 2.38 ( 2015) 19p prop.
-------Can the spun hub allow the boat to work and get up to a high RPM, but just seem sluggish? I thought once that failure happened you would be at limp home low RPM only? I've never experienced this problem before.

Thanks so much for these ideas.

Edited by wbswhaler on 09/14/23 - 5:50 AM

Posted by Phil T on 09/14/23 - 7:50 AM

When they changed the lower unit gear ratio (2015), they had to change the pitch of the prop. It's a math thing. Not related to your issues.

A prop has a large insert that is pressed into the prop that has the correct splines for the engine it is installed on. it also has a shock absorbing material to protect the gear case.

Due to age or hitting an object, the hub can slip at medium to high speeds. It often does not slip at lower speeds.

Do not use any of the original gas. Eliminate that as an issue. Run on fresh fuel.

Given your low rpm's, on reflection, I think the engine is not running on all cylinders. Test each one for spark.

Posted by wbswhaler on 09/15/23 - 7:38 PM

Engine is a 115 XL 4S SN 1B485289 label on the engine says max RPM is 6400.
Gauge on the console only goes to 6000.
I think we got a high RPM alarm on the sea trial.

Would the alarm come from the console gauge reading getting pinned at 6000 or from a sensor in the engine itself??

Posted by Phil T on 09/17/23 - 7:44 AM

Pre 2018, the max hp for the Montauk 170 was 90hp.

A prior owner repowered after the fact and was too lazy or stupid to upgrade the harnesses and gauges.

I would have the rigging inspected for compatibility. If they are re-using the old it may not be displaying correct info.

I find it highly doubtful engine is going 6k at 26 mph.

Go to a Merc dealer (Nauset Marine? )or an independent shop that has Mercury factory trained mech's.

The alarm would come from the key switch on the old rigging.