Motor height - Merc 150 seapro

[ship happens]

@Macdeep

Can you post your numbers quick and dirty? Including prop series, diameter and pitch.

 

[Macdeep]

When you say you don’t use your trim tabs ???do you know what position they are in ?stupid question but I need to ask lol. You should be able to stabilize the boat a bit, nose down or up at one point should ride decent lol, most guys I see going by with porposing, they ride the bow to high, flatten it out and go . Between the motor trim and the trim tabs there should be a sweet spot

Ya, I mean with the previous power (115 4s), I would use my trim tabs at full nose down to get out of the hole, then back them off completely, trim out the outboard and then if necessary touch them a little bit to level the boat, but never had to used them to keep the nose down.

So really I only used the trim tabs for launch, and leveling left to right, never to keep the nose down. I had plenty of fore/aft trim control from the outboard (which had a foil, and needed a foil as it was underpowered).

Now I dont need full tabs for launch, but I use them any way because it gets me level much much faster, and it's my old habit. But with this new set up, once on plane, I need the trim tabs at about half way down (they create some spray) and I cannot release the motor trim at all or I get porpoising.

The porpoising/inability to trim out the outboard at a medium cruise speed is really the issue I'm trying to fight now. The spray issues have subsided considerably since I moved the transducer and added the bow weight/ redistributed my gear to the cuddy lockers rather than under the seats.

But that's for normal cruising speed up to ~25knots and up to 4000rpm. In all cases, whether before I had weight in the bow or not, or whether I had the foil on or not, if I kicked the speed up to 30 knots or higher, this all changes. But I have to say, I don't want to be cruising at 30-35 knots at 4500-5300 RPM. Once I get going that fast, I can release the trim tabs and back them off all the way. And I can trim out the outboard without getting porpoising. Also, no caviatation when going into a tight turn at 30 knots, same as when I go into a tight turn at 20 knots.

So I guess I just have to avoid the medium speed and only travel and high speed? But I'd really rather not. I like 22-26knots and staying under 4000 RPM for noise on deck, fuel burn, safety/reaction time, comfort in light chop etc etc.

For the poster a few back, here's my numbers again.

Prop: Solas Rubex 15.3x19 3Plus 9511-153-19
Outboard: 2025 Merc Seapro 150 (2.08 gear ratio, 4.75" case)
WOT range: 4800-5300
Boat: 18ft Malibu 182 (Cuddy with similar design to the DE185) Max HP hull rating is 175. It's definitely an butt heavy boat with a rounded bottom from the mid point back.

Performance numbers with really any load I've tried so far
3500 - 23mph 20 knots
4000 - 29mph 25-26 knots
4500 - 35mph 30 knots
5200 - 40mph 35knots - This is WOT for this prop and setup with both a 2 passenger medium load full fuel and a 4 passenger load with bow locker ~60 pounts of ballast and all other heavy stuff in the cuddy lockers. I got it to 5300 once under perfect glass conditions and about 20-30 seconds of getting the trim perfect and watching the needle slowly creeping up from 5000. As mentioned, once over 4500RPM I can release the trim tabs and start to trim out the outboard.

No, I don't have an pictures of the spray, cav plate etc when at top speed.

And I wouldn't disagree that I'd get better performance with a different prop. I was offered this prop to test since it's used and at a reasonable price from a prop shop. I think it's well suited for the RPM WOT spec, but I definitely would be interested in a second prop and keep this one as a spare tire, especially if there's some optimizing for stern lift and performance, especially if I raise the motor one last hole to get the cav plate clear of the waterline.

Correct me if I'm wrong, but it seems like to combat the porpoising I need to add more weight to the bow before I go raising the motor another notch, probably go extreme and try another 100lb on top of what I already have there.

I don't think I'll ever enjoy seeing a porpoise again

 

[brutus]

Ya, I mean with the previous power (115 4s), I would use my trim tabs at full nose down to get out of the hole, then back them off completely, trim out the outboard and then if necessary touch them a little bit to level the boat, but never had to used them to keep the nose down.

So really I only used the trim tabs for launch, and leveling left to right, never to keep the nose down. I had plenty of fore/aft trim control from the outboard (which had a foil, and needed a foil as it was underpowered).

Now I dont need full tabs for launch, but I use them any way because it gets me level much much faster, and it's my old habit. But with this new set up, once on plane, I need the trim tabs at about half way down (they create some spray) and I cannot release the motor trim at all or I get porpoising.

The porpoising/inability to trim out the outboard at a medium cruise speed is really the issue I'm trying to fight now. The spray issues have subsided considerably since I moved the transducer and added the bow weight/ redistributed my gear to the cuddy lockers rather than under the seats.

But that's for normal cruising speed up to ~25knots and up to 4000rpm. In all cases, whether before I had weight in the bow or not, or whether I had the foil on or not, if I kicked the speed up to 30 knots or higher, this all changes. But I have to say, I don't want to be cruising at 30-35 knots at 4500-5300 RPM. Once I get going that fast, I can release the trim tabs and back them off all the way. And I can trim out the outboard without getting porpoising. Also, no caviatation when going into a tight turn at 30 knots, same as when I go into a tight turn at 20 knots.

So I guess I just have to avoid the medium speed and only travel and high speed? But I'd really rather not. I like 22-26knots and staying under 4000 RPM for noise on deck, fuel burn, safety/reaction time, comfort in light chop etc etc.

For the poster a few back, here's my numbers again.

Prop: Solas Rubex 15.3x19 3Plus 9511-153-19
Outboard: 2025 Merc Seapro 150 (2.08 gear ratio, 4.75" case)
WOT range: 4800-5300
Boat: 18ft Malibu 182 (Cuddy with similar design to the DE185) Max HP hull rating is 175. It's definitely an butt heavy boat with a rounded bottom from the mid point back.

Performance numbers with really any load I've tried so far
3500 - 23mph 20 knots
4000 - 29mph 25-26 knots
4500 - 35mph 30 knots
5200 - 40mph 35knots - This is WOT for this prop and setup with both a 2 passenger medium load full fuel and a 4 passenger load with bow locker ~60 pounts of ballast and all other heavy stuff in the cuddy lockers. I got it to 5300 once under perfect glass conditions and about 20-30 seconds of getting the trim perfect and watching the needle slowly creeping up from 5000. As mentioned, once over 4500RPM I can release the trim tabs and start to trim out the outboard.

No, I don't have an pictures of the spray, cav plate etc when at top speed.

And I wouldn't disagree that I'd get better performance with a different prop. I was offered this prop to test since it's used and at a reasonable price from a prop shop. I think it's well suited for the RPM WOT spec, but I definitely would be interested in a second prop and keep this one as a spare tire, especially if there's some optimizing for stern lift and performance, especially if I raise the motor one last hole to get the cav plate clear of the waterline.

Correct me if I'm wrong, but it seems like to combat the porpoising I need to add more weight to the bow before I go raising the motor another notch, probably go extreme and try another 100lb on top of what I already have there.

I don't think I'll ever enjoy seeing a porpoise again

I don’t know but 300lbs of weight in the bow on a 18 ft boat seems like a lot . I’ve notice when swap from my Honda to Suzuki 225 to 300, no weight difference, but the suke swings a way bigger prop, my trim range on the suke is way smaller haven’t tried different props, just water grip , started at 21.5 then 19 then 17 pitch, now I am in low end of rpm range,it did bounced a bit( prop pushing the stern down) so moved a bit of weight to the front 100lbs max . I only use my trim tabs to level the boat side to side. To keep your cruising speed where you want it you might have to compensate with your tabs, you will loose efficiency but at least you won’t bounce around. Good luck

 

[SpringVelocity]

There is only one other thing can be throwing things off. I know a couple of guys with my boat had the waterlogged floor/foam thing happen. This was notorious for double eagles.

Have you ever checked?

It seems like you have some weight back there screwing things up. Not saying you have it but it might be worth checking so not your not chasing a ghost so to speak.