20 HP Mercury and 20 HP Tohatsu Racing Propeller

[GoFast Cracker Bay]

The Tohatsu and Mercury 20's are remarkably similar. I wonder if Tohatsu is making them for Mercury or if they started with the same deisgn and made it theirs.

[Mini Max]

The Tohatsu and Mercury 20's are remarkably similar. I wonder if Tohatsu is making them for Mercury or if they started with the same deisgn and made it theirs.

All Mercury badge engines 30 hp and under are manufactured by Tohatsu.

[Ron Hill]

Made some 15, 16 and 17. Reported speeds were 44 with the 17.

[Mini Max]

Made some 15, 16 and 17. Reported speeds were 44 with the 17.

True, but it was a one time, first try with a 480 lb motor, boat and driver. (I am 200) No Tach fitted.

The Carolina Virginia Racing Association has purchased a 4 stroke Tohatsu and commissioned John Runne to build a purpose built runabout. It will be raced and used in their driver school. John has all of the Hill Marine props and will give them a fair test. We think 50 mph is a reasonable expectation.

[Mini Max]

The four stroke engine is legal to race 15SSR and BSR APBA Stock Outboard. 2023 there were 30 drivers scoring points in 15SSR and 0 drivers scoring points in BSR, although 63 drivers scored points in BSH. I assume the wisdom is that the 20 four stroke can race with 15SSR provisionally but when numbers justify then BSR would race as a four stroke 20 class.

[dandrews75]

What rpm were you running and prop diameter? In my opinion we need to build new boats to match the engine. For a utility I’d look closely at the GT15, 30 and Dillon boats for design baseline. For a hydro you need a longer, wider, deeper boat with rear shoes to decrease hull drag. Would also go to a boat mounted water pickup to allow the motor to be jacked up as high as you want. I’m thinking bigger diameter props and keep adding pitch til you hit the rev limiter. Use an adjustable jack plate or transom to make height changes quickly to figure this out quickly. We ran 40+ with 20 Merc’s on tiny titans and flat bottom river racers back in the 70’s and 80’s as kids. The speed is there, just have to unlock it. This is an EFI engine which is totally opposite of a carbed engine in that the carbed motor you can under prop it and spin the hell out of the wheel to get speed out of it. As a point of reference I had a 16 ft crestliner utility with an Evinrude 50 Etec on the back. I quickly found out I could not under prop it, hit the rev limiter right away. I kept putting more pitch to it til it ran out of steam and that was 21p and 46.4 mph. Respectable but given the power to weight ratio should have been able to run 52-55 which I believe could have been achieved with a low water pickup nose cone. So in summary here’s what I would concentrate on; prop match to EFI and new hull with the least amount of drag possible. For a hydro I would use a bigger version of the HARM J boat (same boat that HRL novice drivers built last winter, Karelsen/Kelsen design similar to the 70’s early 80’s boat Ron posted on BRF FB). Wider cockpit, the extended nose on the boat would accommodate hotfoot for sit down ride. Make the seat movable for/aft to help find the balance of the boat. So 10’8”, 40” wide air trap, 2.5 degrees AOA, etc. I see that a group headed by Dewald has decided to adapt a racing foot to the 20 4 stroke. I would say the ROI is not good considering the gains that could be made with a low water pickup nose cone or remote water pickup for a lot less money. Speeds were 51 on the utility and 48 on a hydro. I am certainly not a proponent for a specialized foot and perpetuating the current status quo which does nothing but hinder growth and opportunities in boat racing.

[Mini Max]

Engine height I set with the same APBA Brown height checker I use on my CSR Yamato. CL of prop shaft 3/4" below the bottom. Up to 85 mph the round nose mercury gear case on the 300 hp Mercury's I use on some cats I build is better than the pointy nose low water pickup "Sportmaster" There isn't going to be any gain from spending a lot more money to modify the 4 stroke with parts no longer made.

Yes you might want to use the left hand rotation gear case because of all the props on dusty shelves but the European prop makers LAK and Winrace provided me thru hub exhaust props from the GT-15 classes and Ron Hill sent me over the hub exhaust RH props he made.

The numbers I heard with the 20 four stroke modified with a "A" racing lower unit were the runabout 44 mph and hydro 51 mph. 44 was the speed the first time I tried the box stock Tohatsu with either the European props or the ones Ron made. I come at this as an average guy, not from a racing family. It took me a year to find a good C Yamato 102 and a refurbished D Tohatsu 50. To get the 20 took 15 minutes, the time it took to drive to the marina and take my pick of the ten 20 hp Tohatsu's in stock.