The Boating Forum - 30 mainship pilot " tailwalking i think"

the boat is a semi displacement hull with a single diesel in a prop pocket, it has a sharp entry and a relatively flat stern it has trim tabs which i think are the problem. the transom is rounded so when the tabs are down they are on a angle not running square with the boat which creates spray and unnessary drag.the boats stern moves laterally, in a following sea is the worst but with the tabs up or down the boat still is squirly.even in calm seas when another boat passes me his wake makes my stern move around. the tabs also are 12"x12" which i think are to small. i'm thinking of making larger tabs parallelogram shaped with downward fins so they are running square with the water from under the boat. also i was thinking if a larger rudder would help or adding smart rails the whole length of the boat.does anyone have any experience with this problem.thanks

i doubt its you tabs, i'll assum you have the 4cyl yanmar with a 13knot cruise ? Its basically being underpowered along with hull design.

http://www.thehulltruth.com/archive/t-25760.html

http://www.thehulltruth.com/archive/t-32111.html

http://www.boatdesign.net/forums/powerboats/35-henriques-maine-coaster-tailwalking-problem-following-sea-10884.html


all very similar to your hull.

many round chine semi displacement hulls have following sea issues. Sailboats don't have much issues because of narrow stern and large keel.

trim tabs are not the issue.

the boat has a 315 yanmar with 18 kt. cruise and square chines.

Post the question on the Tabman board and you'll get good answers from people who know tabs and more than likely the boat. They've helped me out in the past.

http://www.thehulltruth.com/tabmans-trim-tab-discussion-15/

I operated my friends mainship many times, same characteristic. I had a friend who has built boats most of his life tell me the main contributor is that the rudder is too small, and that is why the stern tracks back and forth.

thanks flounderpounder did your friend change his rudder and if so what were the results

I had a 34 pilot but with twins. Rode great in any direction.

the boat has a 315 yanmar with 18 kt. cruise and square chines.

If he is doing 18 knots then he shouldn't be effected by following seas. But then again he said semi displacement, and 18 knot cruise is not semi!

FWIW- A friend with a Fortier 26' had the rudder replaced with a custom larger one (semi-balanced) and felt his downsea handling and backing control was signicantly improved with less than a kt cruise loss due to increased drag.

Never put the tabs down in a following sea.
Your problem friend is the hull design. Flat stern, small keel and really small rudder. No rudder in the world is going overcome that hull design in a following sea.

Sick,
No never replaced the rudder, we just learned to anticipate and correct...

Marlin I think they may call them semi-displacement because the market they may want to serve.

Quote from their website:
"Down-East Defined
The romantic retro-styling of the down-east design Pilot 30 belies her high-tech heritage, truly modern interior and superb performance capabilities. While it may be the Pilot 30's dramatic and graceful upward-sloped sheer lines and all-aluminum windshield that first capture your attention, discriminating yachtsmen appreciate the attention to detail and ease of maintenance that sets this trawler in a league all her own. Other key highlights of the Pilot 30 include her durable all-fiberglass exterior construction, straight tracking semi-displacement hull and highly economical single engine diesel options."

A 315 HP diesel and a flat stern are reflected in the 30 mph top speed. The boat will plane a very slow speed, a review said 7.5 kts.

What you have a flat stern boat that will wallow around in any quartering or following sea.
Speed will not over come the tendency to broach (tailwalk) in a following sea.


es her high-tech heritage, truly modern interior and superb performance capabilities. While it may be the Pilot 30's dramatic and graceful upward-sloped sheer lines and all-aluminum windshield that first capture your attention, discriminating yachtsmen appreciate the attention to detail and ease of maintenance that sets this trawler in a league all her own. Other key highlights of the Pilot 30 include her durable all-fiberglass exterior construction, straight tracking semi-displacement hull and highly economical single engine diesel options.