New prop choice and engine height setup

[Cruzey]

Hi all,

I recently purchased a Bermuda Dolphin, essentially a Quintrex Dart 375. I have a short shaft Sea Pro (tohatsu 25/30)

I have all ready removed the carb plate and replaced it with the larger one, and have advanced the timing to 25 degrees as per the 30 hp specs.

I have spoken to a local welding shop as i want to raise the height of the motor. The transom has a very shallow cut out, and running a string line from the bottom with the motor level the cav plate sits 2 inches below. Under way the cav plate is not visible at all.

I'm a bit unsure as to how much to raise the motor by. 2'' should see the plate level with the water, but what happens if i was to go higher. What positive / negative effects would it have if the cav plate is well and truly above water line?

On to the prop, right now i have a Powertech sra which is a 10 inch, but unsure on pitch. They were popular at one stage for surf life saving boats, and i'm thinking the prop is more about holeshot, and mid speed grip / handling designed for use in the surf. So i'm thinking about a chopper instead, Ron Hill makes them to suit in 10 inch in either 15, 16, or 17 pitch.

Ron straight up reccomended the cleaver to suit, but from what i have read you really have to run the motor up high for the cleaver to work, and in which case i'm not sure about the water pick ups, i don't want to modify the nose cone and i also think a cleaver on this style boat is just too far fetched and not realistic.

Can i run a chopper with the standard lower unit and through hub exhaust? I assume the outboard is a through hub?

Modification wise, well i have ordered a tiny tach to keep check in things as i go along. I have found Boyosen do a reed set for about $50 to suit the motor. I also chucked a set of iridiums in this arvo.

Other than that the only thing i can think if without spending a lot of money is shaving the head. I have a spare head here which is brand new, i was quoted somewhere around the $100 mark which i'm more than happy to spend. Problem is though i have no idea on the squish clearance, does anyone know, or a safe way of measuring ? If i was to test the compression now, what is a relatively safe increase to look for? Also in Aus higher octane fuel is readily available.

Prop and height set up is obviously mandatory, other than that my list of mods only comes to about $200, excluding prop obviously, i got a very big discount on the motor so i'm not against spending a little bit on it.

The boat is mainly a recreational set up, with estuary work in mind with one extra person on board and some fishing gear. I just want to get the most out of the boat top end wise without compromising things too much (i.e waiting 2 minutes for a cleaver to hook up in the meantime i have other vessels around and so forth)

Any input would be great !!

Oh and finally, is drilling exhaust relief holes relatively safe? If understand you drill just above the cav plate? I'm new to outboards and i don't understand the whole water going in that area, how the exhaust really works and the section containing the gearbox oil.

[DuckLn]

The SRA 3 blade (SRA3) or 4 blade (SRA4)? You will need to determine pitch which is usually printed on the side of powertech props. The SRA, in my experience, is best when run higher in the water as it will mantain bite at high elevations and on my boat (15 foot flatbottom) I can run the cav plate even with the hull without "blow out problems" wheras other props would not hold a bite at that height. Granted it was 2 mph slower than the stilletto prop but still a nice prop.

[Cruzey]

It's a 10 inch 10 pitch. Second lowest pitch offered in the sra series of props. The prop came with another Tohatsu 25 i had, and was in real good nick and figured it would at least be better than the factory prop. The factory prop though is an 11 pitch, so in theory it's probably slightly quicker at the very top. Weather pending i'm hoping to take the boat out and try the factory prop in the mean time as i also want to test out some other mods.

I have ordered a 10 x 17 chopper anyway through Ron. I've read the motor will spin the 18P to factory redline one up on small inflatables like mini thundercats, so 17 is probably a good starting point and can be worked down a pitch or 2 if need be, and can also have some extra cupping added if the prop won't hook up. I've also drilled 3 relief holes each side above the cav plate so that should help the prop with slip as getting out of the hole can be a little tricky one up.