1999 Sundancer 270 Bravo I/II/III confusion

[StefanFL]

I'm trying to find this out for quite some time without success.

In 1999 according to official documentation base 7.4 mpi was paired with B2 and optionally with B3.
I know that B2 have longer(sits deeper) lower unit, so Im trying to figure out if they were mounted through the same hole on transom, or B2 were mounted higher so that the prop would be on the same height?


Reason I'm asking this is my boat currently have B1, someone changed it before I purchased the boat. I'm not satisfied with performance and I think boat is to heavy for this setup and want to swap, I would prefer B2 as more bullet proof drive, I'm not too worried about idle speed handling or docking I'm used to this boat with single prop.

It's hard to identify what was original drive B2/B3, so if mounting height is same I don't have to worry about that and can safely go with B2 Otherwise I can only go back to original drive.

 

[scoflaw]

B2 is no more Bullitt proof than the B1, they both use the same upper half, where the problems happen. The B3 was the upgrade for the B2. B3 lower will bolt to your upper. B2 pushes a much larger diameter prop than the 1 &3 so it sacrifices speed because of that. Never heard anything about diff. mounting heights

 

[StefanFL]

I know that lower unit is interchangeable as upper is same for all 3 drives, except some models have different oil passages, but the fact that b2 accommodate larger prop diameter let me believe it has to be longer so you have more room from shaft to cavitation plate.

My problem is not speed, It a heavy boat and with current B1 most likely 1:1.5 (have to confirm this) it have a problem getting on plane with full gas/water tank and 2 persons aboard. it goes to 4000-4400wot depends on hull cleanings and water/wind conditions.
With less fuel/water and 2 persons I was able to go around 30mph at wot and still plane at around 3700rpm, however full tanks wot 4000-4400 15-17mph and it's dragging, cant get on plane properly, tabs are not helping much.

I believe it's due to small prop that's not providing enough thrust for a heavy boat.

Since I couldn't find anyone with this setup in similar boat length/weight/hull I thought It would be best to go back to original B2 with original prop and swap for smaller/bigger if necessary.
B3 is more expansive and I wouldn't benefit much for docking handling.

Current prop is Quicksilver vengeance 14 1/2 17P.

If anyone have other suggestions, I would be glad to hear

 

[Lazy Daze]

Think of it this way... the B2 propshaft would be slightly lower than a B1 or B3 propshaft, but the top of the blade would be the same... the bottom of the blade would be slightly lower.

However, the current lower unit/prop does not explain your lack of performance. Something else is going on... damaged running gear, improper trimming, dirty bottom, engine health, etc.

 

[StefanFL]

Thank you for the explanation about bravo 2. I was reaching around and someone wanted to save a buck on replacing bravo 2 lower with SEI B1 clone, and they had a concern that prop will be closer to the surface.
I checked mecruy prop calc and according to them with bravo I should look at 15 1/2 18P 3 blade or 16p 4b.
I can't believe that one in pitch would make that difference.

I will check engine compression just to be sure sure, but I believe I wouldn't go past 4000 if power is issue.
Did tune up recently (plugs/cables/ignition cap/fuel,oil filter/oil)
I tried on the same day before refueling was able to get on plane fairly easily (WOT around 4200), but have to maintain 3700 to stay on plane, after refueling Still same wot but not planning and only 16mph at wot.
Bottom is not spotless has antifooling paint and I did clean it in the water with brush, but had same issue with perfectly clean hull.

My thoughts are if boat is going 21mph@3700 planing and in the other case 16mph@4200mph, either prop is not spining at 1:1.5 rate anymore (don't know how this can be possible) or prop is spinning but don't have enough pickup to push the boat.

Engine health I guess could affect by not having enough mid-range torque/hp to push it on plane at right time, but If I keep it wot at the straight line and it's reaching target RPM it should eventually jump out, but it doesn't.


Off topic (Just as a reference for underpowered):
I have another boat 255ccr that I purchased slightly damaged without engine/drive (had 8.2HO originally) dropped in 5.7 carb 260hp and alpha 1gen2 dont even remember prop pitch as i got the combo cheap taken out from similarly sized boat (i was like if it doesn't work I didn't break a bank so will sell and put bigger engine) It gets on plane really quickly, and plane still plane on 3100 without the problem, even pulling a tube.

 

[Bugsy22]

Experienced similar frustration with our 90' 270 dancer. A big wide heavy boat that Also had a 7.4 bravo 1 power combo. That vengeance is way to small. A large diameter 4 blade prop would go a loonnnggg way on your boat. I tried a Solas Rubex 4 (worked much better than the stock mirage 17) and a Mercury Bravo 1 19p which really made a huge difference. The bravo 1 was pricey but well worth it. Planed easily, cruised around 26kph at about 3400 rpms and was generally just more enjoyable because of hiw much quieter the ride was. The Solas #s were just a bit higher in all respects except cruising speed. It was about 23 kph at 3500rpms.

 

[StefanFL]

Thank you for sharing your experience.
I just checked the specs from model archive from SR website it's 5800lbs vs 7500lbs dry. 9' vs 9'2" bean is not a big difference, but weight seems to be a problem in my case.

Solas is cheap enough to give it a try.
But I strongly believe going to 1:2.0 or even 1:2.2 B2/B3 would be the only solution.
Will do compression test and everything else I can do to confirm that engine is healthy enough to justify replacing the drive for B3, otherwise will probably go with Solas until it can push and think about re-powering along with drive over the winter.

Do you remember what Pitch Solas Rubex was?

 

[scoflaw]

As far as a ratio change, going from 1:5 to 1:2 would be the wrong direction for increasing rpm's

 

[Dave - M]

Ive got the same boat as bugsy describes. I couldnt get on plane last year to save my life (first season in the water). It planed ok with an empty gas tank, no water, no gear but once loaded and ready, forget it. Got my prop off and found it was a 14 x 19 turning point aluminum. I found someone with the same boat, running a Mercury Mirage 15.5 x 17 SS. He had no problems getting on plane so I bought one. Boat gets up easily and runs around 27 mph, 3500 rpms. Not fast maybe, but fast enough to be fun.

One other thing Ive noticed. With tabs down, she struggles and doesnt get up. Tabs up, she climbs out like she should.

 

[StefanFL]

As far as a ratio change, going from 1:5 to 1:2 would be the wrong direction for increasing rpm's

I don't have problem with low rpm, it actually reach 4200-4400 (per spec 4200-4600 is good range). I believe that with 1:1.5 and small prop it's spinning too fast to grab some water to push the boat. With 1:2.0 prop will spin slow and I would be able to use larger prop that can grab more water and hence push the boat properly.

Maybe I didn't explain my problem correctly at the first post.

 

[StefanFL]

Ive got the same boat as bugsy describes. I couldnt get on plane last year to save my life (first season in the water). It planed ok with an empty gas tank, no water, no gear but once loaded and ready, forget it. Got my prop off and found it was a 14 x 19 turning point aluminum. I found someone with the same boat, running a Mercury Mirage 15.5 x 17 SS. He had no problems getting on plane so I bought one. Boat gets up easily and runs around 27 mph, 3500 rpms. Not fast maybe, but fast enough to be fun.

One other thing Ive noticed. With tabs down, she struggles and doesnt get up. Tabs up, she climbs out like she should.

I have 14.5 x 17p SS with the added weight of my boat 1in smaller diameter should be right on spot compared to 15.5 x 17p on roughly same size boat with 1500-2000 pounds less.

I'm thinking if it's possible that engine is reaching wot but not getting all the power, doubt it will spin to over 4000rpm if power is a problem, but who knows.
Logic says if I go bigger diameter I should get more thrust, but on the other hand im not over reving at wot, so larger prop will probably lower wot rpm and I will trade one problem for another

 

[StefanFL]

Update:
Did a test run yesterday and recorded speed of GPS. (forgot my compression tester, so didn't perform compression test yet)
Did the comparison of actual speed vs theoretical to calculate slip and something is way off. picture attached.
Btw. on the way back wife went into the cabin and at wot it went from 17.5-18mph to 20mph.

Test was performed with tabs all the way down and trim all way down. With tabs up performance is worse. bow goes up slightly more, but stern goes down much more.

If I try to trim drive up even slightly while at wot, rpm immediately goes to 4600 but I lose speed.

Previous owner replaced upper unit because clutch was bad, he said they first thought it's prop hub, took it to prop shop and it was ok, so mechanic replaced upper unit.

Any thoughts? I suspect spun hub on prop, at least hopping for quick fix. Can I change prop on bravo 1 in water?

 

[Lazy Daze]

A spun hub is easy enough to ID - just matchmark it. However, I would be surprised if this was the issue given the type of hub it uses. Also, typically a Mirage prop is the one used on a Bravo. Sure - you can change it in the water - just don't drop anything!

Are you 100% positive that the bottom of the hull is perfectly clean - along with the drive/prop? And everything there is in good shape? The RPM shooting up also could be ventilation from damage or fouling.

 

[scoflaw]

Reread post#9. Something is slipping real bad. Try another prop, any prop. Could be a slipping clutch.

 

[StefanFL]

Reread post#9. Something is slipping real bad. Try another prop, any prop. Could be a slipping clutch.

I did, He didn't mention if prop was damaged or just improper. Only difference my boat seems to perform better with tabs down.
I agree something is slipping badly.
I don't have a spare prop, will try to get one before next weekend, hopefully it's not the clutch.
If I don't get my hands on a prop until the weekend or If I get a chance to go earlier, does it make sense to make a tiny line on a prop and nut/shaft end and take it for a ride?
If I understand correctly if prop moves around hub even a little it's shot?
Just trying to figure out if that's in fact a prop and not a clutch, before I spend money on good prop, because don't want to waste money on prop as if I have to change/repair upper for clutch, I might upgrade to B3.
Now if it's in fact only a prop, I will be glad to spend money on a decent prop as long as i can cruise in mid 20s mph at 3200-3600 im cool.

 

[scoflaw]

Checking for a spun hub would be a start. Post #9, he was using a 1" larger diameter than you. Maybe the smaller diameter could be causing the slippage.

 

[StefanFL]

A spun hub is easy enough to ID - just matchmark it. However, I would be surprised if this was the issue given the type of hub it uses. Also, typically a Mirage prop is the one used on a Bravo. Sure - you can change it in the water - just don't drop anything!

Are you 100% positive that the bottom of the hull is perfectly clean - along with the drive/prop? And everything there is in good shape? The RPM shooting up also could be ventilation from damage or fouling.

Missed this post, I don't have Mirage, it's Vengeance 14.5 , Mirage is 15.5 diameter I think.
Drive tabs are clean, bottom is not spotless clean, i scrubbed as much as I could in water.
But had same issue last year toward the end of season with 4 ppl and almost full tank, just wasn't as bad I was hitting 20mph, but I tried to stop and start again and took it on plane with some delay.
This year because of covid I was sparing gas so just trolled to nearest cove to chill and swim, when I tried it first time was 1/4tank planed fine, didn't bother to check gps speed but was over 25 for sure, went back to marina filled gas, and next time problem was back, but much worse no plane at all.

Another weird fact is now if trim it just a little bit rpm spikes like crazy, last year even with added weight trimming didnt cause this.
Is it possible that trim has a leak somewhere and trim actuator actually expends when boat is going forward? this would cause it to be too close to surface and little trim makes it over rev?

 

[Lazy Daze]

Is it possible that trim has a leak somewhere and trim actuator actually expends when boat is going forward? this would cause it to be too close to surface and little trim makes it over rev?

No - that's not it.

You can go ahead and matchmark the prop - but as I mentioned, you don't have a traditional hub in there. I have never heard of the hub type you have spinning ('course, doesn't mean it can't) - and I would think it would be much more noticeable - probably making a noise and some vibration. Pulling the prop and visually inspecting the hub should answer any questions. Then again, you have a light-duty prop on a torquey motor.

BUT... usually when a prop hub (or the coupler) is starting to spin, it spins when trying to get on plane with full throttle since that puts a lot of stress on the prop - and it seems you don't have that problem.

Since you also said you didn't have this issue before, and while it still may not be the "best" prop for your boat, it sure sounds like something else is going on - like ventilation.

 

[StefanFL]

Yes it's definitely not the perfect prop for this boat, but fixing the current issue first and testing it in working condition with not great performance will make it easier to decide which prop to buy.
I ordered Quicksilver flo torq II for alpha/bravo1 applications, so will see how it goes.
According to design of hub I order it doesn't look like it can spin like this , on the other hand locking/safety washer that's currently on the prop it looks completely differently from this one, only kit I found online with this style locking washer is some knonk off up to 150hp hub, so hopefully that's inside currently and just spun.

Inspected the prop itself and it looks good, nothing looks bend etc, no damages, not even a scratches.

what else can cause ventilation?

 

[StefanFL]

went to change the hub and see if that's my problem. got flo torq II 835257q1 as per spec for bravo I and vengeance prop. well it's not the same, the one in prop seems to be metal on metal..
Still don't know if it can slip