Tohatsu MFS 20 transom height test run

[Packard8]

Hi folks,

I had the new skiff (Bolger Diablo 15 footer) out yesterday for the maiden voyage. The motor is the short shaft version and the skiff has a 15" transom. After reading threads here I checked the AV plane (also equipped with a "Doel-fin" stabilizer fin) with the bottom of the boat and they are within 1/4 of the same.

The boat gets on the plane quickly and after running several directions (upwind, downwind, crosswind) at WOT it maxed out at 24 MPH on the GPS. This is about what I expected, as forums familiar with this hull say to expect about one MPH per HP of the motor if it is propped and running correctly.

Attached are photos of the spray off of the higher secondary fin...it was mostly horizontal with me at the helm, slightly more towards vertical with a friend (about 20 lbs heavier than me) driving. Does this look about right? I am thinking of another run with maybe 1/2 inch shim on the transom before drilling the mounting holes.

Thanks,

John

 

[Sea Rider]

Re: Tohatsu MFS 20 transom height test run

Assume you have engine set/trimed to be perpendicular to boat once floating without passengers, right ? If so, seat mate near bow to distribute weight evenly. If flow is passing slightly under small upper plate, you are in the sweet spot. Leave it there if you already have achieved this condition. For fine tunning perform test on flat calm no windy waters.

http://www.youtube.com/watch?v=oBeZjaA76VM&feature=youtu.be

Happy Boating

 

[Packard8]

Re: Tohatsu MFS 20 transom height test run

Thanks SR,

I'm getting a bit more spray off the upper plate compared to the video you linked to. I'll try about a 1/2 inch shim and compare.

Cheers,

John

 

[Sea Rider]

Re: Tohatsu MFS 20 transom height test run

You are welcome John,

We usually test boats without helms, mate at front and tiller driver becomes a spotter, check water flow, shim height what's needed and thats all. With boat well trimed and ballanced, you should target to have a clean near flat spray under small upper plate at wot. Is the mate who took the pic the one who is driving ? If having helm at middle with mate at front to have a well ballanced combo, have another boat follow side to you, and check your water flow.

Happy Boating

 

[Packard8]

Re: Tohatsu MFS 20 transom height test run

Thanks SR,

I just put a 1/2" shim on the transom and moved the trim rod up one hole. This puts the lower AV plate just about perfect in both height and parallel to the flat of the keel. Hope to do another test drive shortly. Wish I had a tach, are there relative inexpensive ones available for the Tohatsu MFS 20? I think the only practical use would be for testing @ WOT, otherwise I have a pretty good feel and ear for the sweet spot where I'm making good speed and the motor is running "easy".

Also this boat is tiller steer only. I took the photos seated about 1 ft forward of the transom, and my friend was seated on the center thwart.

Thanks,

John

 

[Sea Rider]

Re: Tohatsu MFS 20 transom height test run

One gadget that is must have installed is a hour/tach meter. Hour meter for checking total worked hours and excellent for preventive maintenences. Tach for wot test, select other prop pitch and adjust slow idle rpm. Check Hardline or Tiny Tach, piece of cake to install as both are induction type.

You can gain up to 200-300 more rpm with correct trim/height transom installation, better boat performance and lessen fuel consumption. Install a tach go for a wot spin and check if inside working parameters factory stated.

With passengers, engine, boat well ballanced combo, doel fin/cav plate and hull must ride paralell to water level once at plane. Trim at hole angle to achieve this setting.

Happy Boating

 

[Packard8]

Re: Tohatsu MFS 20 transom height test run

Thanks SR,

Hope to get her back on the water soon to compare the new transom shim & trim settings. Also looking for some 2-3 foot chop to test the handling. The Sacramento river near Rio Vista often has some more challenging water compared to the lakes around here and is only 4 or 5 miles from the launch ramp.

Thanks for your advice!

John

 

[Sea Rider]

Re: Tohatsu MFS 20 transom height test run

Also looking for some 2-3 foot chop to test the handling.

John, once you get trim/transom engine height set correctly tested/adjusted on plain flat waters, that engine will work awesome at any sea conditions, the only issue is that you cannot ride that hard at plane on high chop because of unconfortable bumpy ride and kidney's issues.

Happy Boating