Prop for 23 SeaCraft with transom-mounted Merc 250 EFI

[rdoaner123]

Hello,

Does anyone have any suggestions for this setup? The SeaCraft is a 1978, and the Merc 250 EFI Offshore is from 1996.

I'm currently running a 17 pitch Mirage Plus, and am only getting 5,400 rpm and 46/47 mph with an empty boat.

Another thing is the prop blows out on turns, and the engine still needs to be raised a hole or two. Thoughts?

[Bigshrimpin]

What's your goal?


I would get the engine height set correctly first. It sounds like you are close. The mirage plus is a large diameter lower rake prop (15.5") and it does blowout pretty easily.


Rev4 17p will hold a lot better, but you might lose a few RPM's over the mirage plus 17p.

I personally would try an 18p Enertia (non Eco) which are faster than the mirage plus and hold a lot better.

19p Highfive is a very small diameter prop that's good in the low to mid range. That prop can ride high and won't blow out.



I ran a 225hp 3.0L carb Mariner with a 17p Rev4 for a week (before I sold the engine). Running light I could get into the high 40's trimmed up.





On the current engine 150hp Merc 4 stroke . . . I either run a 15p Enertia or 17p Highfive (depending on load).

[rdoaner123]

Appreciate the reply! I'm shooting for a prop that gets me to at least 5,600rpm, and doesn't blow out. Good hole shot is a strong plus, as well as high cruising and top end speed.

What rpms were you turning on the 225 with the 17p rev4?

[Bigshrimpin]

If I remember correctly it was 5800rpms. That 3.0L engine drank fuel. I could believe how much it used. I put a 2.4L frankenmerc back on after that one until I repowered with the 150.

[rdoaner123]

Originally Posted by Bigshrimpin

If I remember correctly it was 5800rpms. That 3.0L engine drank fuel. I could believe how much it used. I put a 2.4L frankenmerc back on after that one until I repowered with the 150.

How can it be that your 225hp motor turned a prop at 5800 rpm when my 250 can only turn and easier-to-turn prop at 5,400 rpm? Is there something wrong with my motor?

[Capt Terry]

Originally Posted by rdoaner123

How can it be that your 225hp motor turned a prop at 5800 rpm when my 250 can only turn and easier-to-turn prop at 5,400 rpm? Is there something wrong with my motor?

There may be a difference in gear ratios like there was between Bushwacker’s 150 ETEC and my 150 HO ETEC, both on 20’ Seafaris. I dont remember the details but his liked the Cyclone better than mine, so he bought it. I had better low speed control at 17 mph and achieved the desired WOT RPM with a 17p High Five.

[kmoose]

Rev 4 is the direction I would go.

[joshmon71]

i have a 17p mirage plus getting dusty once i put on a 17p rev4 never went back. probably could have gone higher in height. the 17P blew out on hard turns. i lost 2-3mph and 200-300 rpm i think but don't have hard numbers at hand. wot speed less worried about than making sure engine can get into its proper wot rpm's. i can spin to 6k/6100 rpm heavy loaded trimmed up and more light load. 6400 is max. verado 275, 650lb motor. t-top.

looks like next winter I need to think about a pilot house for another major project. i've never ever seen over 42/43 light load.

have a new (to me its a 2020 merc 300) engine this season so prob go to a 18p rev4. that highfive though is interesting....hmmmm.....i like the stern lift of the rev 4.

Bigshrimpin How is the high 5 prop running in seas east of the cape / offshore compared to rev4? planes out about same speed?

that is one sweet pilot house Bigshrimpin! wowza! is that a seamark? they are out of business now? went looking around for them a few years back came up blank.

[rdoaner123]

I should mention, I've been noticing the prop sometimes partially breaks free even when I'm going in a straight line and increase rpms. The prop shaft seems straight, so I'm not sure why this would be

Attached is a picture of the lower unit with slightly positive trim at 3600rpm. I circled the back of the anti-ventilation plate in red. You can barely see it through the water. Should I go up one hole or two?

[joshmon71]

I love my Rev4. Never went back to a mirage plus. same issue as you cavitated with M+ only on turns. 250 Verado had a17P R4, and was just barely getting WOT needed. When I sourced a 275 ECU it was perfect peachy with a 17P R4 so you are probably right its on the edge of a 17P or 15P R4. Turns out I could have gone much higher with the R4....never did raise from 2008- till this season with a one year old used 300 Verado i snagged.

No idea why or where read (tht? and propgod?), but the 15P Rev4 had some reason for not being advisable desirable.

Raise you engine even more and get a R4 17P....I suppose you could go silly $$ and get a R4 XP 17P....

Right now, 300 V8, R4, running a 19P R4 heavy load and barely if even need to trim up, hitting 6K which is max end of WOT range. DO have tabs. I had the marina raise the engine so high I was sure it would need to go back down. I was wrong. Those R4s can really run high. I am debating a 20P or even 21P R4 for this summer.

GL, def some art and voodo to propping, heights.