Prop or motor height

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Pahkah

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Have a parker 1800, had a new Honda 100hp put on. Only able to get 5500 RPM (33mph) at WOT with the factory honda 13.25x17 aluminum prop. Cruise at 4400 RPM (24mph). These numbers are fully loaded, with 3 guys, gear, ice, etc. Doesn't seem to matter if motor is trimmed up or down, same results. No trim tabs on boat.

Now the question is, is my motor mounted too low? Or should I try a different prop? From what I've read/seen my motor does seem low. Only problem is I would have to drill new holes as when it was mounted they didn't leave me any wiggle room to raise it.

Also I did try a stainless honda turbo 13.25x15 prop and my numbers got worse. But this was a used prop so maybe something was out of tune?

Thoughts?
 

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I'm assuming your talking about top end. Whats the spec on the max RPM? (6000?) Loaded you not far off for 100HP
Check the rigging that its allowing true WOT.
Go for a run with just you.
 
using the trim square up the plate so it runs parallel then use a straight edge board on the keel. You should be no more than an inch above for the sweet spot.
Yours looks low but its hard to tell from that pic with the broom handle.
 
judging from your 2nd pic there doesnt look like theres any room to go up because the lower mounting bolts appear to not have enough room to go up a full hole.
Yea I mentioned that in my post that would have to drill new holes if need to raise. I will take some new pics of it squared up
 
Take her for a run with someone else in the boat with you. When you are running take a look at the anti-cavitation (A-C) plate. It should be on the top of the water (maybe a little water running over it). Once that is set then start looking at props. I posted this pic on another thread; but, you can clearly see the A-C plates on top of the water. This gives you the least in water drag.
IMG_0637.jpeg
 
Here's another pic, not sure if it helps or not or if I just need to get out there and take a pic while underway. I guess it seems to be within the right range
20210331_160531.jpg
 
looks too high but that wouldnt be slowing down your rpm's
but yes, take a look while underway
Anti cavitation plate is still below the level, but only by an inch, so should be considered to be on the low side. Can see it thru the holes of level. But not sure if that's enough difference to make it worthwhile to drill new holes. Guess I will try a stainless 13.25x17 prop next as well and see what I get.
 
Are you holding the level parallel to the hull or are you holding it level? The measurement should be taken with a straight edge pressed against (parallel) to the running surface. If this is the case the engine is too low. The AC plate should be about an inch higher for every foot past the transom.
 
my bad, i didnt see the plate behind the level. I was looking above it which is why i said too high.
But yes, you need a longer straight edge. A decent 2x4 would serve this purpose.
 
Are you holding the level parallel to the hull or are you holding it level? The measurement should be taken with a straight edge pressed against (parallel) to the running surface. If this is the case the engine is too low. The AC plate should be about an inch higher for every foot past the transom.
Took out the longer level today and ran it along the running surface and squared up the motor to that. The cavitation plate sits 1 3/4" below that line. So looks like I have some drilling to do.

My thought was to drill out the new bottom hole. Remove bottom bolt, insert into new hole. Then remove top bolt and use the jack of the trailer to lift it up. Sound about right?

Hopefully once raised I will have access to the old hole to fill with dowel/tex marine. Otherwise I'm kinda screwed
 
You can lift the engine using the trailer jack like you suggested with wood blocks to support the lower. I would definitely have another person with me. One on the jack one watching the engine. Also use some straps going from the engine to the rear cleats so it doesn't fall backwards.

Any hole in the transom should be filled permanently. I would make sure the transom is good and dry around the old hole and fiberglass it back in. If you need more room around the old hole you can take the mount bracket to the highest setting temporarily, then move back to the height you want after the repair.

Looking at your initial pictures again, you may want the engine mounted on the highest hole to give you the 1"up per 1' back lift. Make sure when you drill the new hole it is high enough for you to be able to do that.
 
Figured I would give an update. Finally got out on the water again this past weekend and snapped a pic while up on plane. She's not trimmed out at all in the pic. But seems to be a tad low.

Unfortunately I took a look in the bilge and now I see why they mounted the bottom bolts in that spot. It can't go any higher below deck. Do you guys have the bottom bolts coming thru above deck near the scuppers?

20210508_123753.jpg
 
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